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* [PATCH] locking/rwsem: Remove arch specific rwsem files
@ 2019-02-11  2:00 Waiman Long
  2019-02-11  2:08 ` Waiman Long
                   ` (2 more replies)
  0 siblings, 3 replies; 13+ messages in thread
From: Waiman Long @ 2019-02-11  2:00 UTC (permalink / raw)
  To: Peter Zijlstra, Ingo Molnar, Will Deacon, Thomas Gleixner
  Cc: linux-kernel, linux-alpha, linux-arm-kernel, linux-hexagon,
	linux-ia64, linuxppc-dev, linux-sh, sparclinux, linux-xtensa,
	linux-arch, x86, Arnd Bergmann, Borislav Petkov, H. Peter Anvin,
	Davidlohr Bueso, Linus Torvalds, Andrew Morton, Tim Chen,
	Waiman Long

As the generic rwsem-xadd code is using the appropriate acquire and
release versions of the atomic operations, the arch specific rwsem.h
files will not be that much faster than the generic code as long as the
atomic functions are properly implemented. So we can remove those arch
specific rwsem.h and stop building asm/rwsem.h to reduce maintenance
effort.

Currently, only x86, alpha and ia64 have implemented architecture
specific fast paths. I don't have access to alpha and ia64 systems for
testing, but they are legacy systems that are not likely to be updated
to the latest kernel anyway.

By using a rwsem microbenchmark, the total locking rates on a 4-socket
56-core 112-thread x86-64 system before and after the patch were as
follows (mixed means equal # of read and write locks):

                      Before Patch              After Patch
   # of Threads  wlock   rlock   mixed     wlock   rlock   mixed
   ------------  -----   -----   -----     -----   -----   -----
        1        27,373  29,409  28,170    28,773  30,164  29,276
        2         7,697  14,922   1,703     7,435  15,167   1,729
        4         6,987  14,285   1,490     7,181  14,438   1,330
        8         6,650  13,652     761     6,918  13,796     718
       16         6,434  15,729     713     6,554  16,030     625
       32         5,590  15,312     552     6,124  15,344     471
       64         5,980  15,478      61     5,668  15,509      58

There were some run-to-run variations for the multi-thread tests. For
x86-64, using the generic C code fast path seems to be a liitle bit
faster than the assembly version especially for read-lock and when lock
contention is low.  Looking at the assembly version of the fast paths,
there are assembly to/from C code wrappers that save and restore all
the callee-clobbered registers (7 registers on x86-64). The assembly
generated from the generic C code doesn't need to do that. That may
explain the slight performance gain here.

The generic asm rwsem.h can also be merged into kernel/locking/rwsem.h
as no other code other than those under kernel/locking needs to access
the internal rwsem macros and functions.

Signed-off-by: Waiman Long <longman@redhat.com>
---
 MAINTAINERS                     |   1 -
 arch/alpha/include/asm/rwsem.h  | 211 -----------------------------------
 arch/arm/include/asm/Kbuild     |   1 -
 arch/arm64/include/asm/Kbuild   |   1 -
 arch/hexagon/include/asm/Kbuild |   1 -
 arch/ia64/include/asm/rwsem.h   | 172 -----------------------------
 arch/powerpc/include/asm/Kbuild |   1 -
 arch/s390/include/asm/Kbuild    |   1 -
 arch/sh/include/asm/Kbuild      |   1 -
 arch/sparc/include/asm/Kbuild   |   1 -
 arch/x86/include/asm/rwsem.h    | 237 ----------------------------------------
 arch/x86/lib/Makefile           |   1 -
 arch/x86/lib/rwsem.S            | 156 --------------------------
 arch/xtensa/include/asm/Kbuild  |   1 -
 include/asm-generic/rwsem.h     | 140 ------------------------
 include/linux/rwsem.h           |   4 +-
 kernel/locking/percpu-rwsem.c   |   2 +
 kernel/locking/rwsem.h          | 130 ++++++++++++++++++++++
 18 files changed, 133 insertions(+), 929 deletions(-)
 delete mode 100644 arch/alpha/include/asm/rwsem.h
 delete mode 100644 arch/ia64/include/asm/rwsem.h
 delete mode 100644 arch/x86/include/asm/rwsem.h
 delete mode 100644 arch/x86/lib/rwsem.S
 delete mode 100644 include/asm-generic/rwsem.h

diff --git a/MAINTAINERS b/MAINTAINERS
index 9919840..053f536 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -8926,7 +8926,6 @@ F:	arch/*/include/asm/spinlock*.h
 F:	include/linux/rwlock*.h
 F:	include/linux/mutex*.h
 F:	include/linux/rwsem*.h
-F:	arch/*/include/asm/rwsem.h
 F:	include/linux/seqlock.h
 F:	lib/locking*.[ch]
 F:	kernel/locking/
diff --git a/arch/alpha/include/asm/rwsem.h b/arch/alpha/include/asm/rwsem.h
deleted file mode 100644
index cf8fc8f9..0000000
--- a/arch/alpha/include/asm/rwsem.h
+++ /dev/null
@@ -1,211 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0 */
-#ifndef _ALPHA_RWSEM_H
-#define _ALPHA_RWSEM_H
-
-/*
- * Written by Ivan Kokshaysky <ink@jurassic.park.msu.ru>, 2001.
- * Based on asm-alpha/semaphore.h and asm-i386/rwsem.h
- */
-
-#ifndef _LINUX_RWSEM_H
-#error "please don't include asm/rwsem.h directly, use linux/rwsem.h instead"
-#endif
-
-#ifdef __KERNEL__
-
-#include <linux/compiler.h>
-
-#define RWSEM_UNLOCKED_VALUE		0x0000000000000000L
-#define RWSEM_ACTIVE_BIAS		0x0000000000000001L
-#define RWSEM_ACTIVE_MASK		0x00000000ffffffffL
-#define RWSEM_WAITING_BIAS		(-0x0000000100000000L)
-#define RWSEM_ACTIVE_READ_BIAS		RWSEM_ACTIVE_BIAS
-#define RWSEM_ACTIVE_WRITE_BIAS		(RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
-
-static inline int ___down_read(struct rw_semaphore *sem)
-{
-	long oldcount;
-#ifndef	CONFIG_SMP
-	oldcount = sem->count.counter;
-	sem->count.counter += RWSEM_ACTIVE_READ_BIAS;
-#else
-	long temp;
-	__asm__ __volatile__(
-	"1:	ldq_l	%0,%1\n"
-	"	addq	%0,%3,%2\n"
-	"	stq_c	%2,%1\n"
-	"	beq	%2,2f\n"
-	"	mb\n"
-	".subsection 2\n"
-	"2:	br	1b\n"
-	".previous"
-	:"=&r" (oldcount), "=m" (sem->count), "=&r" (temp)
-	:"Ir" (RWSEM_ACTIVE_READ_BIAS), "m" (sem->count) : "memory");
-#endif
-	return (oldcount < 0);
-}
-
-static inline void __down_read(struct rw_semaphore *sem)
-{
-	if (unlikely(___down_read(sem)))
-		rwsem_down_read_failed(sem);
-}
-
-static inline int __down_read_killable(struct rw_semaphore *sem)
-{
-	if (unlikely(___down_read(sem)))
-		if (IS_ERR(rwsem_down_read_failed_killable(sem)))
-			return -EINTR;
-
-	return 0;
-}
-
-/*
- * trylock for reading -- returns 1 if successful, 0 if contention
- */
-static inline int __down_read_trylock(struct rw_semaphore *sem)
-{
-	long old, new, res;
-
-	res = atomic_long_read(&sem->count);
-	do {
-		new = res + RWSEM_ACTIVE_READ_BIAS;
-		if (new <= 0)
-			break;
-		old = res;
-		res = atomic_long_cmpxchg(&sem->count, old, new);
-	} while (res != old);
-	return res >= 0 ? 1 : 0;
-}
-
-static inline long ___down_write(struct rw_semaphore *sem)
-{
-	long oldcount;
-#ifndef	CONFIG_SMP
-	oldcount = sem->count.counter;
-	sem->count.counter += RWSEM_ACTIVE_WRITE_BIAS;
-#else
-	long temp;
-	__asm__ __volatile__(
-	"1:	ldq_l	%0,%1\n"
-	"	addq	%0,%3,%2\n"
-	"	stq_c	%2,%1\n"
-	"	beq	%2,2f\n"
-	"	mb\n"
-	".subsection 2\n"
-	"2:	br	1b\n"
-	".previous"
-	:"=&r" (oldcount), "=m" (sem->count), "=&r" (temp)
-	:"Ir" (RWSEM_ACTIVE_WRITE_BIAS), "m" (sem->count) : "memory");
-#endif
-	return oldcount;
-}
-
-static inline void __down_write(struct rw_semaphore *sem)
-{
-	if (unlikely(___down_write(sem)))
-		rwsem_down_write_failed(sem);
-}
-
-static inline int __down_write_killable(struct rw_semaphore *sem)
-{
-	if (unlikely(___down_write(sem))) {
-		if (IS_ERR(rwsem_down_write_failed_killable(sem)))
-			return -EINTR;
-	}
-
-	return 0;
-}
-
-/*
- * trylock for writing -- returns 1 if successful, 0 if contention
- */
-static inline int __down_write_trylock(struct rw_semaphore *sem)
-{
-	long ret = atomic_long_cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
-			   RWSEM_ACTIVE_WRITE_BIAS);
-	if (ret == RWSEM_UNLOCKED_VALUE)
-		return 1;
-	return 0;
-}
-
-static inline void __up_read(struct rw_semaphore *sem)
-{
-	long oldcount;
-#ifndef	CONFIG_SMP
-	oldcount = sem->count.counter;
-	sem->count.counter -= RWSEM_ACTIVE_READ_BIAS;
-#else
-	long temp;
-	__asm__ __volatile__(
-	"	mb\n"
-	"1:	ldq_l	%0,%1\n"
-	"	subq	%0,%3,%2\n"
-	"	stq_c	%2,%1\n"
-	"	beq	%2,2f\n"
-	".subsection 2\n"
-	"2:	br	1b\n"
-	".previous"
-	:"=&r" (oldcount), "=m" (sem->count), "=&r" (temp)
-	:"Ir" (RWSEM_ACTIVE_READ_BIAS), "m" (sem->count) : "memory");
-#endif
-	if (unlikely(oldcount < 0))
-		if ((int)oldcount - RWSEM_ACTIVE_READ_BIAS == 0)
-			rwsem_wake(sem);
-}
-
-static inline void __up_write(struct rw_semaphore *sem)
-{
-	long count;
-#ifndef	CONFIG_SMP
-	sem->count.counter -= RWSEM_ACTIVE_WRITE_BIAS;
-	count = sem->count.counter;
-#else
-	long temp;
-	__asm__ __volatile__(
-	"	mb\n"
-	"1:	ldq_l	%0,%1\n"
-	"	subq	%0,%3,%2\n"
-	"	stq_c	%2,%1\n"
-	"	beq	%2,2f\n"
-	"	subq	%0,%3,%0\n"
-	".subsection 2\n"
-	"2:	br	1b\n"
-	".previous"
-	:"=&r" (count), "=m" (sem->count), "=&r" (temp)
-	:"Ir" (RWSEM_ACTIVE_WRITE_BIAS), "m" (sem->count) : "memory");
-#endif
-	if (unlikely(count))
-		if ((int)count == 0)
-			rwsem_wake(sem);
-}
-
-/*
- * downgrade write lock to read lock
- */
-static inline void __downgrade_write(struct rw_semaphore *sem)
-{
-	long oldcount;
-#ifndef	CONFIG_SMP
-	oldcount = sem->count.counter;
-	sem->count.counter -= RWSEM_WAITING_BIAS;
-#else
-	long temp;
-	__asm__ __volatile__(
-	"1:	ldq_l	%0,%1\n"
-	"	addq	%0,%3,%2\n"
-	"	stq_c	%2,%1\n"
-	"	beq	%2,2f\n"
-	"	mb\n"
-	".subsection 2\n"
-	"2:	br	1b\n"
-	".previous"
-	:"=&r" (oldcount), "=m" (sem->count), "=&r" (temp)
-	:"Ir" (-RWSEM_WAITING_BIAS), "m" (sem->count) : "memory");
-#endif
-	if (unlikely(oldcount < 0))
-		rwsem_downgrade_wake(sem);
-}
-
-#endif /* __KERNEL__ */
-#endif /* _ALPHA_RWSEM_H */
diff --git a/arch/arm/include/asm/Kbuild b/arch/arm/include/asm/Kbuild
index 1d66db9..989e1a7 100644
--- a/arch/arm/include/asm/Kbuild
+++ b/arch/arm/include/asm/Kbuild
@@ -12,7 +12,6 @@ generic-y += mm-arch-hooks.h
 generic-y += msi.h
 generic-y += parport.h
 generic-y += preempt.h
-generic-y += rwsem.h
 generic-y += seccomp.h
 generic-y += segment.h
 generic-y += serial.h
diff --git a/arch/arm64/include/asm/Kbuild b/arch/arm64/include/asm/Kbuild
index 1e17ea5..60a933b 100644
--- a/arch/arm64/include/asm/Kbuild
+++ b/arch/arm64/include/asm/Kbuild
@@ -16,7 +16,6 @@ generic-y += mm-arch-hooks.h
 generic-y += msi.h
 generic-y += qrwlock.h
 generic-y += qspinlock.h
-generic-y += rwsem.h
 generic-y += segment.h
 generic-y += serial.h
 generic-y += set_memory.h
diff --git a/arch/hexagon/include/asm/Kbuild b/arch/hexagon/include/asm/Kbuild
index b25fd42..0a12feb 100644
--- a/arch/hexagon/include/asm/Kbuild
+++ b/arch/hexagon/include/asm/Kbuild
@@ -26,7 +26,6 @@ generic-y += mm-arch-hooks.h
 generic-y += pci.h
 generic-y += percpu.h
 generic-y += preempt.h
-generic-y += rwsem.h
 generic-y += sections.h
 generic-y += segment.h
 generic-y += serial.h
diff --git a/arch/ia64/include/asm/rwsem.h b/arch/ia64/include/asm/rwsem.h
deleted file mode 100644
index 9179106..0000000
--- a/arch/ia64/include/asm/rwsem.h
+++ /dev/null
@@ -1,172 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0 */
-/*
- * R/W semaphores for ia64
- *
- * Copyright (C) 2003 Ken Chen <kenneth.w.chen@intel.com>
- * Copyright (C) 2003 Asit Mallick <asit.k.mallick@intel.com>
- * Copyright (C) 2005 Christoph Lameter <cl@linux.com>
- *
- * Based on asm-i386/rwsem.h and other architecture implementation.
- *
- * The MSW of the count is the negated number of active writers and
- * waiting lockers, and the LSW is the total number of active locks.
- *
- * The lock count is initialized to 0 (no active and no waiting lockers).
- *
- * When a writer subtracts WRITE_BIAS, it'll get 0xffffffff00000001 for
- * the case of an uncontended lock. Readers increment by 1 and see a positive
- * value when uncontended, negative if there are writers (and maybe) readers
- * waiting (in which case it goes to sleep).
- */
-
-#ifndef _ASM_IA64_RWSEM_H
-#define _ASM_IA64_RWSEM_H
-
-#ifndef _LINUX_RWSEM_H
-#error "Please don't include <asm/rwsem.h> directly, use <linux/rwsem.h> instead."
-#endif
-
-#include <asm/intrinsics.h>
-
-#define RWSEM_UNLOCKED_VALUE		__IA64_UL_CONST(0x0000000000000000)
-#define RWSEM_ACTIVE_BIAS		(1L)
-#define RWSEM_ACTIVE_MASK		(0xffffffffL)
-#define RWSEM_WAITING_BIAS		(-0x100000000L)
-#define RWSEM_ACTIVE_READ_BIAS		RWSEM_ACTIVE_BIAS
-#define RWSEM_ACTIVE_WRITE_BIAS		(RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
-
-/*
- * lock for reading
- */
-static inline int
-___down_read (struct rw_semaphore *sem)
-{
-	long result = ia64_fetchadd8_acq((unsigned long *)&sem->count.counter, 1);
-
-	return (result < 0);
-}
-
-static inline void
-__down_read (struct rw_semaphore *sem)
-{
-	if (___down_read(sem))
-		rwsem_down_read_failed(sem);
-}
-
-static inline int
-__down_read_killable (struct rw_semaphore *sem)
-{
-	if (___down_read(sem))
-		if (IS_ERR(rwsem_down_read_failed_killable(sem)))
-			return -EINTR;
-
-	return 0;
-}
-
-/*
- * lock for writing
- */
-static inline long
-___down_write (struct rw_semaphore *sem)
-{
-	long old, new;
-
-	do {
-		old = atomic_long_read(&sem->count);
-		new = old + RWSEM_ACTIVE_WRITE_BIAS;
-	} while (atomic_long_cmpxchg_acquire(&sem->count, old, new) != old);
-
-	return old;
-}
-
-static inline void
-__down_write (struct rw_semaphore *sem)
-{
-	if (___down_write(sem))
-		rwsem_down_write_failed(sem);
-}
-
-static inline int
-__down_write_killable (struct rw_semaphore *sem)
-{
-	if (___down_write(sem)) {
-		if (IS_ERR(rwsem_down_write_failed_killable(sem)))
-			return -EINTR;
-	}
-
-	return 0;
-}
-
-/*
- * unlock after reading
- */
-static inline void
-__up_read (struct rw_semaphore *sem)
-{
-	long result = ia64_fetchadd8_rel((unsigned long *)&sem->count.counter, -1);
-
-	if (result < 0 && (--result & RWSEM_ACTIVE_MASK) == 0)
-		rwsem_wake(sem);
-}
-
-/*
- * unlock after writing
- */
-static inline void
-__up_write (struct rw_semaphore *sem)
-{
-	long old, new;
-
-	do {
-		old = atomic_long_read(&sem->count);
-		new = old - RWSEM_ACTIVE_WRITE_BIAS;
-	} while (atomic_long_cmpxchg_release(&sem->count, old, new) != old);
-
-	if (new < 0 && (new & RWSEM_ACTIVE_MASK) == 0)
-		rwsem_wake(sem);
-}
-
-/*
- * trylock for reading -- returns 1 if successful, 0 if contention
- */
-static inline int
-__down_read_trylock (struct rw_semaphore *sem)
-{
-	long tmp;
-	while ((tmp = atomic_long_read(&sem->count)) >= 0) {
-		if (tmp == atomic_long_cmpxchg_acquire(&sem->count, tmp, tmp+1)) {
-			return 1;
-		}
-	}
-	return 0;
-}
-
-/*
- * trylock for writing -- returns 1 if successful, 0 if contention
- */
-static inline int
-__down_write_trylock (struct rw_semaphore *sem)
-{
-	long tmp = atomic_long_cmpxchg_acquire(&sem->count,
-			RWSEM_UNLOCKED_VALUE, RWSEM_ACTIVE_WRITE_BIAS);
-	return tmp == RWSEM_UNLOCKED_VALUE;
-}
-
-/*
- * downgrade write lock to read lock
- */
-static inline void
-__downgrade_write (struct rw_semaphore *sem)
-{
-	long old, new;
-
-	do {
-		old = atomic_long_read(&sem->count);
-		new = old - RWSEM_WAITING_BIAS;
-	} while (atomic_long_cmpxchg_release(&sem->count, old, new) != old);
-
-	if (old < 0)
-		rwsem_downgrade_wake(sem);
-}
-
-#endif /* _ASM_IA64_RWSEM_H */
diff --git a/arch/powerpc/include/asm/Kbuild b/arch/powerpc/include/asm/Kbuild
index 77ff7fb..75bd77a 100644
--- a/arch/powerpc/include/asm/Kbuild
+++ b/arch/powerpc/include/asm/Kbuild
@@ -9,6 +9,5 @@ generic-y += irq_work.h
 generic-y += local64.h
 generic-y += mcs_spinlock.h
 generic-y += preempt.h
-generic-y += rwsem.h
 generic-y += vtime.h
 generic-y += msi.h
diff --git a/arch/s390/include/asm/Kbuild b/arch/s390/include/asm/Kbuild
index e323977..4b77b42 100644
--- a/arch/s390/include/asm/Kbuild
+++ b/arch/s390/include/asm/Kbuild
@@ -21,7 +21,6 @@ generic-y += local64.h
 generic-y += mcs_spinlock.h
 generic-y += mm-arch-hooks.h
 generic-y += preempt.h
-generic-y += rwsem.h
 generic-y += trace_clock.h
 generic-y += unaligned.h
 generic-y += word-at-a-time.h
diff --git a/arch/sh/include/asm/Kbuild b/arch/sh/include/asm/Kbuild
index a6ef3fe..b89fce4 100644
--- a/arch/sh/include/asm/Kbuild
+++ b/arch/sh/include/asm/Kbuild
@@ -16,7 +16,6 @@ generic-y += mm-arch-hooks.h
 generic-y += parport.h
 generic-y += percpu.h
 generic-y += preempt.h
-generic-y += rwsem.h
 generic-y += serial.h
 generic-y += sizes.h
 generic-y += trace_clock.h
diff --git a/arch/sparc/include/asm/Kbuild b/arch/sparc/include/asm/Kbuild
index b82f64e..e843fc0 100644
--- a/arch/sparc/include/asm/Kbuild
+++ b/arch/sparc/include/asm/Kbuild
@@ -17,7 +17,6 @@ generic-y += mm-arch-hooks.h
 generic-y += module.h
 generic-y += msi.h
 generic-y += preempt.h
-generic-y += rwsem.h
 generic-y += serial.h
 generic-y += trace_clock.h
 generic-y += word-at-a-time.h
diff --git a/arch/x86/include/asm/rwsem.h b/arch/x86/include/asm/rwsem.h
deleted file mode 100644
index 4c25cf6..0000000
--- a/arch/x86/include/asm/rwsem.h
+++ /dev/null
@@ -1,237 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0 */
-/* rwsem.h: R/W semaphores implemented using XADD/CMPXCHG for i486+
- *
- * Written by David Howells (dhowells@redhat.com).
- *
- * Derived from asm-x86/semaphore.h
- *
- *
- * The MSW of the count is the negated number of active writers and waiting
- * lockers, and the LSW is the total number of active locks
- *
- * The lock count is initialized to 0 (no active and no waiting lockers).
- *
- * When a writer subtracts WRITE_BIAS, it'll get 0xffff0001 for the case of an
- * uncontended lock. This can be determined because XADD returns the old value.
- * Readers increment by 1 and see a positive value when uncontended, negative
- * if there are writers (and maybe) readers waiting (in which case it goes to
- * sleep).
- *
- * The value of WAITING_BIAS supports up to 32766 waiting processes. This can
- * be extended to 65534 by manually checking the whole MSW rather than relying
- * on the S flag.
- *
- * The value of ACTIVE_BIAS supports up to 65535 active processes.
- *
- * This should be totally fair - if anything is waiting, a process that wants a
- * lock will go to the back of the queue. When the currently active lock is
- * released, if there's a writer at the front of the queue, then that and only
- * that will be woken up; if there's a bunch of consecutive readers at the
- * front, then they'll all be woken up, but no other readers will be.
- */
-
-#ifndef _ASM_X86_RWSEM_H
-#define _ASM_X86_RWSEM_H
-
-#ifndef _LINUX_RWSEM_H
-#error "please don't include asm/rwsem.h directly, use linux/rwsem.h instead"
-#endif
-
-#ifdef __KERNEL__
-#include <asm/asm.h>
-
-/*
- * The bias values and the counter type limits the number of
- * potential readers/writers to 32767 for 32 bits and 2147483647
- * for 64 bits.
- */
-
-#ifdef CONFIG_X86_64
-# define RWSEM_ACTIVE_MASK		0xffffffffL
-#else
-# define RWSEM_ACTIVE_MASK		0x0000ffffL
-#endif
-
-#define RWSEM_UNLOCKED_VALUE		0x00000000L
-#define RWSEM_ACTIVE_BIAS		0x00000001L
-#define RWSEM_WAITING_BIAS		(-RWSEM_ACTIVE_MASK-1)
-#define RWSEM_ACTIVE_READ_BIAS		RWSEM_ACTIVE_BIAS
-#define RWSEM_ACTIVE_WRITE_BIAS		(RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
-
-/*
- * lock for reading
- */
-#define ____down_read(sem, slow_path)					\
-({									\
-	struct rw_semaphore* ret;					\
-	asm volatile("# beginning down_read\n\t"			\
-		     LOCK_PREFIX _ASM_INC "(%[sem])\n\t"		\
-		     /* adds 0x00000001 */				\
-		     "  jns        1f\n"				\
-		     "  call " slow_path "\n"				\
-		     "1:\n\t"						\
-		     "# ending down_read\n\t"				\
-		     : "+m" (sem->count), "=a" (ret),			\
-			ASM_CALL_CONSTRAINT				\
-		     : [sem] "a" (sem)					\
-		     : "memory", "cc");					\
-	ret;								\
-})
-
-static inline void __down_read(struct rw_semaphore *sem)
-{
-	____down_read(sem, "call_rwsem_down_read_failed");
-}
-
-static inline int __down_read_killable(struct rw_semaphore *sem)
-{
-	if (IS_ERR(____down_read(sem, "call_rwsem_down_read_failed_killable")))
-		return -EINTR;
-	return 0;
-}
-
-/*
- * trylock for reading -- returns 1 if successful, 0 if contention
- */
-static inline bool __down_read_trylock(struct rw_semaphore *sem)
-{
-	long result, tmp;
-	asm volatile("# beginning __down_read_trylock\n\t"
-		     "  mov          %[count],%[result]\n\t"
-		     "1:\n\t"
-		     "  mov          %[result],%[tmp]\n\t"
-		     "  add          %[inc],%[tmp]\n\t"
-		     "  jle	     2f\n\t"
-		     LOCK_PREFIX "  cmpxchg  %[tmp],%[count]\n\t"
-		     "  jnz	     1b\n\t"
-		     "2:\n\t"
-		     "# ending __down_read_trylock\n\t"
-		     : [count] "+m" (sem->count), [result] "=&a" (result),
-		       [tmp] "=&r" (tmp)
-		     : [inc] "i" (RWSEM_ACTIVE_READ_BIAS)
-		     : "memory", "cc");
-	return result >= 0;
-}
-
-/*
- * lock for writing
- */
-#define ____down_write(sem, slow_path)			\
-({							\
-	long tmp;					\
-	struct rw_semaphore* ret;			\
-							\
-	asm volatile("# beginning down_write\n\t"	\
-		     LOCK_PREFIX "  xadd      %[tmp],(%[sem])\n\t"	\
-		     /* adds 0xffff0001, returns the old value */ \
-		     "  test " __ASM_SEL(%w1,%k1) "," __ASM_SEL(%w1,%k1) "\n\t" \
-		     /* was the active mask 0 before? */\
-		     "  jz        1f\n"			\
-		     "  call " slow_path "\n"		\
-		     "1:\n"				\
-		     "# ending down_write"		\
-		     : "+m" (sem->count), [tmp] "=d" (tmp),	\
-		       "=a" (ret), ASM_CALL_CONSTRAINT	\
-		     : [sem] "a" (sem), "[tmp]" (RWSEM_ACTIVE_WRITE_BIAS) \
-		     : "memory", "cc");			\
-	ret;						\
-})
-
-static inline void __down_write(struct rw_semaphore *sem)
-{
-	____down_write(sem, "call_rwsem_down_write_failed");
-}
-
-static inline int __down_write_killable(struct rw_semaphore *sem)
-{
-	if (IS_ERR(____down_write(sem, "call_rwsem_down_write_failed_killable")))
-		return -EINTR;
-
-	return 0;
-}
-
-/*
- * trylock for writing -- returns 1 if successful, 0 if contention
- */
-static inline bool __down_write_trylock(struct rw_semaphore *sem)
-{
-	bool result;
-	long tmp0, tmp1;
-	asm volatile("# beginning __down_write_trylock\n\t"
-		     "  mov          %[count],%[tmp0]\n\t"
-		     "1:\n\t"
-		     "  test " __ASM_SEL(%w1,%k1) "," __ASM_SEL(%w1,%k1) "\n\t"
-		     /* was the active mask 0 before? */
-		     "  jnz          2f\n\t"
-		     "  mov          %[tmp0],%[tmp1]\n\t"
-		     "  add          %[inc],%[tmp1]\n\t"
-		     LOCK_PREFIX "  cmpxchg  %[tmp1],%[count]\n\t"
-		     "  jnz	     1b\n\t"
-		     "2:\n\t"
-		     CC_SET(e)
-		     "# ending __down_write_trylock\n\t"
-		     : [count] "+m" (sem->count), [tmp0] "=&a" (tmp0),
-		       [tmp1] "=&r" (tmp1), CC_OUT(e) (result)
-		     : [inc] "er" (RWSEM_ACTIVE_WRITE_BIAS)
-		     : "memory");
-	return result;
-}
-
-/*
- * unlock after reading
- */
-static inline void __up_read(struct rw_semaphore *sem)
-{
-	long tmp;
-	asm volatile("# beginning __up_read\n\t"
-		     LOCK_PREFIX "  xadd      %[tmp],(%[sem])\n\t"
-		     /* subtracts 1, returns the old value */
-		     "  jns        1f\n\t"
-		     "  call call_rwsem_wake\n" /* expects old value in %edx */
-		     "1:\n"
-		     "# ending __up_read\n"
-		     : "+m" (sem->count), [tmp] "=d" (tmp)
-		     : [sem] "a" (sem), "[tmp]" (-RWSEM_ACTIVE_READ_BIAS)
-		     : "memory", "cc");
-}
-
-/*
- * unlock after writing
- */
-static inline void __up_write(struct rw_semaphore *sem)
-{
-	long tmp;
-	asm volatile("# beginning __up_write\n\t"
-		     LOCK_PREFIX "  xadd      %[tmp],(%[sem])\n\t"
-		     /* subtracts 0xffff0001, returns the old value */
-		     "  jns        1f\n\t"
-		     "  call call_rwsem_wake\n" /* expects old value in %edx */
-		     "1:\n\t"
-		     "# ending __up_write\n"
-		     : "+m" (sem->count), [tmp] "=d" (tmp)
-		     : [sem] "a" (sem), "[tmp]" (-RWSEM_ACTIVE_WRITE_BIAS)
-		     : "memory", "cc");
-}
-
-/*
- * downgrade write lock to read lock
- */
-static inline void __downgrade_write(struct rw_semaphore *sem)
-{
-	asm volatile("# beginning __downgrade_write\n\t"
-		     LOCK_PREFIX _ASM_ADD "%[inc],(%[sem])\n\t"
-		     /*
-		      * transitions 0xZZZZ0001 -> 0xYYYY0001 (i386)
-		      *     0xZZZZZZZZ00000001 -> 0xYYYYYYYY00000001 (x86_64)
-		      */
-		     "  jns       1f\n\t"
-		     "  call call_rwsem_downgrade_wake\n"
-		     "1:\n\t"
-		     "# ending __downgrade_write\n"
-		     : "+m" (sem->count)
-		     : [sem] "a" (sem), [inc] "er" (-RWSEM_WAITING_BIAS)
-		     : "memory", "cc");
-}
-
-#endif /* __KERNEL__ */
-#endif /* _ASM_X86_RWSEM_H */
diff --git a/arch/x86/lib/Makefile b/arch/x86/lib/Makefile
index 140e618..9866520 100644
--- a/arch/x86/lib/Makefile
+++ b/arch/x86/lib/Makefile
@@ -23,7 +23,6 @@ obj-$(CONFIG_SMP) += msr-smp.o cache-smp.o
 lib-y := delay.o misc.o cmdline.o cpu.o
 lib-y += usercopy_$(BITS).o usercopy.o getuser.o putuser.o
 lib-y += memcpy_$(BITS).o
-lib-$(CONFIG_RWSEM_XCHGADD_ALGORITHM) += rwsem.o
 lib-$(CONFIG_INSTRUCTION_DECODER) += insn.o inat.o insn-eval.o
 lib-$(CONFIG_RANDOMIZE_BASE) += kaslr.o
 lib-$(CONFIG_FUNCTION_ERROR_INJECTION)	+= error-inject.o
diff --git a/arch/x86/lib/rwsem.S b/arch/x86/lib/rwsem.S
deleted file mode 100644
index dc2ab6e..0000000
--- a/arch/x86/lib/rwsem.S
+++ /dev/null
@@ -1,156 +0,0 @@
-/*
- * x86 semaphore implementation.
- *
- * (C) Copyright 1999 Linus Torvalds
- *
- * Portions Copyright 1999 Red Hat, Inc.
- *
- *	This program is free software; you can redistribute it and/or
- *	modify it under the terms of the GNU General Public License
- *	as published by the Free Software Foundation; either version
- *	2 of the License, or (at your option) any later version.
- *
- * rw semaphores implemented November 1999 by Benjamin LaHaise <bcrl@kvack.org>
- */
-
-#include <linux/linkage.h>
-#include <asm/alternative-asm.h>
-#include <asm/frame.h>
-
-#define __ASM_HALF_REG(reg)	__ASM_SEL(reg, e##reg)
-#define __ASM_HALF_SIZE(inst)	__ASM_SEL(inst##w, inst##l)
-
-#ifdef CONFIG_X86_32
-
-/*
- * The semaphore operations have a special calling sequence that
- * allow us to do a simpler in-line version of them. These routines
- * need to convert that sequence back into the C sequence when
- * there is contention on the semaphore.
- *
- * %eax contains the semaphore pointer on entry. Save the C-clobbered
- * registers (%eax, %edx and %ecx) except %eax which is either a return
- * value or just gets clobbered. Same is true for %edx so make sure GCC
- * reloads it after the slow path, by making it hold a temporary, for
- * example see ____down_write().
- */
-
-#define save_common_regs \
-	pushl %ecx
-
-#define restore_common_regs \
-	popl %ecx
-
-	/* Avoid uglifying the argument copying x86-64 needs to do. */
-	.macro movq src, dst
-	.endm
-
-#else
-
-/*
- * x86-64 rwsem wrappers
- *
- * This interfaces the inline asm code to the slow-path
- * C routines. We need to save the call-clobbered regs
- * that the asm does not mark as clobbered, and move the
- * argument from %rax to %rdi.
- *
- * NOTE! We don't need to save %rax, because the functions
- * will always return the semaphore pointer in %rax (which
- * is also the input argument to these helpers)
- *
- * The following can clobber %rdx because the asm clobbers it:
- *   call_rwsem_down_write_failed
- *   call_rwsem_wake
- * but %rdi, %rsi, %rcx, %r8-r11 always need saving.
- */
-
-#define save_common_regs \
-	pushq %rdi; \
-	pushq %rsi; \
-	pushq %rcx; \
-	pushq %r8;  \
-	pushq %r9;  \
-	pushq %r10; \
-	pushq %r11
-
-#define restore_common_regs \
-	popq %r11; \
-	popq %r10; \
-	popq %r9; \
-	popq %r8; \
-	popq %rcx; \
-	popq %rsi; \
-	popq %rdi
-
-#endif
-
-/* Fix up special calling conventions */
-ENTRY(call_rwsem_down_read_failed)
-	FRAME_BEGIN
-	save_common_regs
-	__ASM_SIZE(push,) %__ASM_REG(dx)
-	movq %rax,%rdi
-	call rwsem_down_read_failed
-	__ASM_SIZE(pop,) %__ASM_REG(dx)
-	restore_common_regs
-	FRAME_END
-	ret
-ENDPROC(call_rwsem_down_read_failed)
-
-ENTRY(call_rwsem_down_read_failed_killable)
-	FRAME_BEGIN
-	save_common_regs
-	__ASM_SIZE(push,) %__ASM_REG(dx)
-	movq %rax,%rdi
-	call rwsem_down_read_failed_killable
-	__ASM_SIZE(pop,) %__ASM_REG(dx)
-	restore_common_regs
-	FRAME_END
-	ret
-ENDPROC(call_rwsem_down_read_failed_killable)
-
-ENTRY(call_rwsem_down_write_failed)
-	FRAME_BEGIN
-	save_common_regs
-	movq %rax,%rdi
-	call rwsem_down_write_failed
-	restore_common_regs
-	FRAME_END
-	ret
-ENDPROC(call_rwsem_down_write_failed)
-
-ENTRY(call_rwsem_down_write_failed_killable)
-	FRAME_BEGIN
-	save_common_regs
-	movq %rax,%rdi
-	call rwsem_down_write_failed_killable
-	restore_common_regs
-	FRAME_END
-	ret
-ENDPROC(call_rwsem_down_write_failed_killable)
-
-ENTRY(call_rwsem_wake)
-	FRAME_BEGIN
-	/* do nothing if still outstanding active readers */
-	__ASM_HALF_SIZE(dec) %__ASM_HALF_REG(dx)
-	jnz 1f
-	save_common_regs
-	movq %rax,%rdi
-	call rwsem_wake
-	restore_common_regs
-1:	FRAME_END
-	ret
-ENDPROC(call_rwsem_wake)
-
-ENTRY(call_rwsem_downgrade_wake)
-	FRAME_BEGIN
-	save_common_regs
-	__ASM_SIZE(push,) %__ASM_REG(dx)
-	movq %rax,%rdi
-	call rwsem_downgrade_wake
-	__ASM_SIZE(pop,) %__ASM_REG(dx)
-	restore_common_regs
-	FRAME_END
-	ret
-ENDPROC(call_rwsem_downgrade_wake)
diff --git a/arch/xtensa/include/asm/Kbuild b/arch/xtensa/include/asm/Kbuild
index e255683..7026b37 100644
--- a/arch/xtensa/include/asm/Kbuild
+++ b/arch/xtensa/include/asm/Kbuild
@@ -23,7 +23,6 @@ generic-y += mm-arch-hooks.h
 generic-y += param.h
 generic-y += percpu.h
 generic-y += preempt.h
-generic-y += rwsem.h
 generic-y += sections.h
 generic-y += topology.h
 generic-y += trace_clock.h
diff --git a/include/asm-generic/rwsem.h b/include/asm-generic/rwsem.h
deleted file mode 100644
index 93e67a0..0000000
--- a/include/asm-generic/rwsem.h
+++ /dev/null
@@ -1,140 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0 */
-#ifndef _ASM_GENERIC_RWSEM_H
-#define _ASM_GENERIC_RWSEM_H
-
-#ifndef _LINUX_RWSEM_H
-#error "Please don't include <asm/rwsem.h> directly, use <linux/rwsem.h> instead."
-#endif
-
-#ifdef __KERNEL__
-
-/*
- * R/W semaphores originally for PPC using the stuff in lib/rwsem.c.
- * Adapted largely from include/asm-i386/rwsem.h
- * by Paul Mackerras <paulus@samba.org>.
- */
-
-/*
- * the semaphore definition
- */
-#ifdef CONFIG_64BIT
-# define RWSEM_ACTIVE_MASK		0xffffffffL
-#else
-# define RWSEM_ACTIVE_MASK		0x0000ffffL
-#endif
-
-#define RWSEM_UNLOCKED_VALUE		0x00000000L
-#define RWSEM_ACTIVE_BIAS		0x00000001L
-#define RWSEM_WAITING_BIAS		(-RWSEM_ACTIVE_MASK-1)
-#define RWSEM_ACTIVE_READ_BIAS		RWSEM_ACTIVE_BIAS
-#define RWSEM_ACTIVE_WRITE_BIAS		(RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
-
-/*
- * lock for reading
- */
-static inline void __down_read(struct rw_semaphore *sem)
-{
-	if (unlikely(atomic_long_inc_return_acquire(&sem->count) <= 0))
-		rwsem_down_read_failed(sem);
-}
-
-static inline int __down_read_killable(struct rw_semaphore *sem)
-{
-	if (unlikely(atomic_long_inc_return_acquire(&sem->count) <= 0)) {
-		if (IS_ERR(rwsem_down_read_failed_killable(sem)))
-			return -EINTR;
-	}
-
-	return 0;
-}
-
-static inline int __down_read_trylock(struct rw_semaphore *sem)
-{
-	long tmp;
-
-	while ((tmp = atomic_long_read(&sem->count)) >= 0) {
-		if (tmp == atomic_long_cmpxchg_acquire(&sem->count, tmp,
-				   tmp + RWSEM_ACTIVE_READ_BIAS)) {
-			return 1;
-		}
-	}
-	return 0;
-}
-
-/*
- * lock for writing
- */
-static inline void __down_write(struct rw_semaphore *sem)
-{
-	long tmp;
-
-	tmp = atomic_long_add_return_acquire(RWSEM_ACTIVE_WRITE_BIAS,
-					     &sem->count);
-	if (unlikely(tmp != RWSEM_ACTIVE_WRITE_BIAS))
-		rwsem_down_write_failed(sem);
-}
-
-static inline int __down_write_killable(struct rw_semaphore *sem)
-{
-	long tmp;
-
-	tmp = atomic_long_add_return_acquire(RWSEM_ACTIVE_WRITE_BIAS,
-					     &sem->count);
-	if (unlikely(tmp != RWSEM_ACTIVE_WRITE_BIAS))
-		if (IS_ERR(rwsem_down_write_failed_killable(sem)))
-			return -EINTR;
-	return 0;
-}
-
-static inline int __down_write_trylock(struct rw_semaphore *sem)
-{
-	long tmp;
-
-	tmp = atomic_long_cmpxchg_acquire(&sem->count, RWSEM_UNLOCKED_VALUE,
-		      RWSEM_ACTIVE_WRITE_BIAS);
-	return tmp == RWSEM_UNLOCKED_VALUE;
-}
-
-/*
- * unlock after reading
- */
-static inline void __up_read(struct rw_semaphore *sem)
-{
-	long tmp;
-
-	tmp = atomic_long_dec_return_release(&sem->count);
-	if (unlikely(tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0))
-		rwsem_wake(sem);
-}
-
-/*
- * unlock after writing
- */
-static inline void __up_write(struct rw_semaphore *sem)
-{
-	if (unlikely(atomic_long_sub_return_release(RWSEM_ACTIVE_WRITE_BIAS,
-						    &sem->count) < 0))
-		rwsem_wake(sem);
-}
-
-/*
- * downgrade write lock to read lock
- */
-static inline void __downgrade_write(struct rw_semaphore *sem)
-{
-	long tmp;
-
-	/*
-	 * When downgrading from exclusive to shared ownership,
-	 * anything inside the write-locked region cannot leak
-	 * into the read side. In contrast, anything in the
-	 * read-locked region is ok to be re-ordered into the
-	 * write side. As such, rely on RELEASE semantics.
-	 */
-	tmp = atomic_long_add_return_release(-RWSEM_WAITING_BIAS, &sem->count);
-	if (tmp < 0)
-		rwsem_downgrade_wake(sem);
-}
-
-#endif	/* __KERNEL__ */
-#endif	/* _ASM_GENERIC_RWSEM_H */
diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h
index 67dbb57..6e56006 100644
--- a/include/linux/rwsem.h
+++ b/include/linux/rwsem.h
@@ -57,15 +57,13 @@ struct rw_semaphore {
 extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *);
 extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
 
-/* Include the arch specific part */
-#include <asm/rwsem.h>
-
 /* In all implementations count != 0 means locked */
 static inline int rwsem_is_locked(struct rw_semaphore *sem)
 {
 	return atomic_long_read(&sem->count) != 0;
 }
 
+#define RWSEM_UNLOCKED_VALUE		0L
 #define __RWSEM_INIT_COUNT(name)	.count = ATOMIC_LONG_INIT(RWSEM_UNLOCKED_VALUE)
 #endif
 
diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c
index 883cf1b..f17dad9 100644
--- a/kernel/locking/percpu-rwsem.c
+++ b/kernel/locking/percpu-rwsem.c
@@ -7,6 +7,8 @@
 #include <linux/sched.h>
 #include <linux/errno.h>
 
+#include "rwsem.h"
+
 int __percpu_init_rwsem(struct percpu_rw_semaphore *sem,
 			const char *name, struct lock_class_key *rwsem_key)
 {
diff --git a/kernel/locking/rwsem.h b/kernel/locking/rwsem.h
index bad2bca..067e265 100644
--- a/kernel/locking/rwsem.h
+++ b/kernel/locking/rwsem.h
@@ -32,6 +32,26 @@
 # define DEBUG_RWSEMS_WARN_ON(c)
 #endif
 
+/*
+ * R/W semaphores originally for PPC using the stuff in lib/rwsem.c.
+ * Adapted largely from include/asm-i386/rwsem.h
+ * by Paul Mackerras <paulus@samba.org>.
+ */
+
+/*
+ * the semaphore definition
+ */
+#ifdef CONFIG_64BIT
+# define RWSEM_ACTIVE_MASK		0xffffffffL
+#else
+# define RWSEM_ACTIVE_MASK		0x0000ffffL
+#endif
+
+#define RWSEM_ACTIVE_BIAS		0x00000001L
+#define RWSEM_WAITING_BIAS		(-RWSEM_ACTIVE_MASK-1)
+#define RWSEM_ACTIVE_READ_BIAS		RWSEM_ACTIVE_BIAS
+#define RWSEM_ACTIVE_WRITE_BIAS		(RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
+
 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
 /*
  * All writes to owner are protected by WRITE_ONCE() to make sure that
@@ -132,3 +152,113 @@ static inline void rwsem_clear_reader_owned(struct rw_semaphore *sem)
 {
 }
 #endif
+
+#ifdef CONFIG_RWSEM_XCHGADD_ALGORITHM
+/*
+ * lock for reading
+ */
+static inline void __down_read(struct rw_semaphore *sem)
+{
+	if (unlikely(atomic_long_inc_return_acquire(&sem->count) <= 0))
+		rwsem_down_read_failed(sem);
+}
+
+static inline int __down_read_killable(struct rw_semaphore *sem)
+{
+	if (unlikely(atomic_long_inc_return_acquire(&sem->count) <= 0)) {
+		if (IS_ERR(rwsem_down_read_failed_killable(sem)))
+			return -EINTR;
+	}
+
+	return 0;
+}
+
+static inline int __down_read_trylock(struct rw_semaphore *sem)
+{
+	long tmp;
+
+	while ((tmp = atomic_long_read(&sem->count)) >= 0) {
+		if (tmp == atomic_long_cmpxchg_acquire(&sem->count, tmp,
+				   tmp + RWSEM_ACTIVE_READ_BIAS)) {
+			return 1;
+		}
+	}
+	return 0;
+}
+
+/*
+ * lock for writing
+ */
+static inline void __down_write(struct rw_semaphore *sem)
+{
+	long tmp;
+
+	tmp = atomic_long_add_return_acquire(RWSEM_ACTIVE_WRITE_BIAS,
+					     &sem->count);
+	if (unlikely(tmp != RWSEM_ACTIVE_WRITE_BIAS))
+		rwsem_down_write_failed(sem);
+}
+
+static inline int __down_write_killable(struct rw_semaphore *sem)
+{
+	long tmp;
+
+	tmp = atomic_long_add_return_acquire(RWSEM_ACTIVE_WRITE_BIAS,
+					     &sem->count);
+	if (unlikely(tmp != RWSEM_ACTIVE_WRITE_BIAS))
+		if (IS_ERR(rwsem_down_write_failed_killable(sem)))
+			return -EINTR;
+	return 0;
+}
+
+static inline int __down_write_trylock(struct rw_semaphore *sem)
+{
+	long tmp;
+
+	tmp = atomic_long_cmpxchg_acquire(&sem->count, RWSEM_UNLOCKED_VALUE,
+		      RWSEM_ACTIVE_WRITE_BIAS);
+	return tmp == RWSEM_UNLOCKED_VALUE;
+}
+
+/*
+ * unlock after reading
+ */
+static inline void __up_read(struct rw_semaphore *sem)
+{
+	long tmp;
+
+	tmp = atomic_long_dec_return_release(&sem->count);
+	if (unlikely(tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0))
+		rwsem_wake(sem);
+}
+
+/*
+ * unlock after writing
+ */
+static inline void __up_write(struct rw_semaphore *sem)
+{
+	if (unlikely(atomic_long_sub_return_release(RWSEM_ACTIVE_WRITE_BIAS,
+						    &sem->count) < 0))
+		rwsem_wake(sem);
+}
+
+/*
+ * downgrade write lock to read lock
+ */
+static inline void __downgrade_write(struct rw_semaphore *sem)
+{
+	long tmp;
+
+	/*
+	 * When downgrading from exclusive to shared ownership,
+	 * anything inside the write-locked region cannot leak
+	 * into the read side. In contrast, anything in the
+	 * read-locked region is ok to be re-ordered into the
+	 * write side. As such, rely on RELEASE semantics.
+	 */
+	tmp = atomic_long_add_return_release(-RWSEM_WAITING_BIAS, &sem->count);
+	if (tmp < 0)
+		rwsem_downgrade_wake(sem);
+}
+
+#endif /* CONFIG_RWSEM_XCHGADD_ALGORITHM */
-- 
1.8.3.1


^ permalink raw reply	[flat|nested] 13+ messages in thread

* Re: [PATCH] locking/rwsem: Remove arch specific rwsem files
  2019-02-11  2:00 [PATCH] locking/rwsem: Remove arch specific rwsem files Waiman Long
@ 2019-02-11  2:08 ` Waiman Long
  2019-02-11  7:11   ` Ingo Molnar
  2019-02-11  9:36 ` Peter Zijlstra
  2019-02-11 11:58 ` Peter Zijlstra
  2 siblings, 1 reply; 13+ messages in thread
From: Waiman Long @ 2019-02-11  2:08 UTC (permalink / raw)
  To: Peter Zijlstra, Ingo Molnar, Will Deacon, Thomas Gleixner
  Cc: linux-kernel, linux-alpha, linux-arm-kernel, linux-hexagon,
	linux-ia64, linuxppc-dev, linux-sh, sparclinux, linux-xtensa,
	linux-arch, x86, Arnd Bergmann, Borislav Petkov, H. Peter Anvin,
	Davidlohr Bueso, Linus Torvalds, Andrew Morton, Tim Chen

On 02/10/2019 09:00 PM, Waiman Long wrote:
> As the generic rwsem-xadd code is using the appropriate acquire and
> release versions of the atomic operations, the arch specific rwsem.h
> files will not be that much faster than the generic code as long as the
> atomic functions are properly implemented. So we can remove those arch
> specific rwsem.h and stop building asm/rwsem.h to reduce maintenance
> effort.
>
> Currently, only x86, alpha and ia64 have implemented architecture
> specific fast paths. I don't have access to alpha and ia64 systems for
> testing, but they are legacy systems that are not likely to be updated
> to the latest kernel anyway.
>
> By using a rwsem microbenchmark, the total locking rates on a 4-socket
> 56-core 112-thread x86-64 system before and after the patch were as
> follows (mixed means equal # of read and write locks):
>
>                       Before Patch              After Patch
>    # of Threads  wlock   rlock   mixed     wlock   rlock   mixed
>    ------------  -----   -----   -----     -----   -----   -----
>         1        27,373  29,409  28,170    28,773  30,164  29,276
>         2         7,697  14,922   1,703     7,435  15,167   1,729
>         4         6,987  14,285   1,490     7,181  14,438   1,330
>         8         6,650  13,652     761     6,918  13,796     718
>        16         6,434  15,729     713     6,554  16,030     625
>        32         5,590  15,312     552     6,124  15,344     471
>        64         5,980  15,478      61     5,668  15,509      58
>
> There were some run-to-run variations for the multi-thread tests. For
> x86-64, using the generic C code fast path seems to be a liitle bit
> faster than the assembly version especially for read-lock and when lock
> contention is low.  Looking at the assembly version of the fast paths,
> there are assembly to/from C code wrappers that save and restore all
> the callee-clobbered registers (7 registers on x86-64). The assembly
> generated from the generic C code doesn't need to do that. That may
> explain the slight performance gain here.
>
> The generic asm rwsem.h can also be merged into kernel/locking/rwsem.h
> as no other code other than those under kernel/locking needs to access
> the internal rwsem macros and functions.
>
> Signed-off-by: Waiman Long <longman@redhat.com>

I have decided to break the rwsem patchset that I sent out on last
Thursday into 3 parts. This patch is part 0 as it touches a number of
arch specific files and so have the widest distribution. I would like to
get it merged first. Part 1 will be patches 1-10 (except 4) of my
original rwsem patchset. This part moves things around, adds more
debugging capability and lays the ground work for the next part. Part 2
will contains the remaining patches which are the real beef of the whole
patchset.

Cheers,
Longman


^ permalink raw reply	[flat|nested] 13+ messages in thread

* Re: [PATCH] locking/rwsem: Remove arch specific rwsem files
  2019-02-11  2:08 ` Waiman Long
@ 2019-02-11  7:11   ` Ingo Molnar
  2019-02-11 10:39     ` Ingo Molnar
  0 siblings, 1 reply; 13+ messages in thread
From: Ingo Molnar @ 2019-02-11  7:11 UTC (permalink / raw)
  To: Waiman Long
  Cc: Peter Zijlstra, Ingo Molnar, Will Deacon, Thomas Gleixner,
	linux-kernel, linux-alpha, linux-arm-kernel, linux-hexagon,
	linux-ia64, linuxppc-dev, linux-sh, sparclinux, linux-xtensa,
	linux-arch, x86, Arnd Bergmann, Borislav Petkov, H. Peter Anvin,
	Davidlohr Bueso, Linus Torvalds, Andrew Morton, Tim Chen


* Waiman Long <longman@redhat.com> wrote:

> On 02/10/2019 09:00 PM, Waiman Long wrote:
> > As the generic rwsem-xadd code is using the appropriate acquire and
> > release versions of the atomic operations, the arch specific rwsem.h
> > files will not be that much faster than the generic code as long as the
> > atomic functions are properly implemented. So we can remove those arch
> > specific rwsem.h and stop building asm/rwsem.h to reduce maintenance
> > effort.
> >
> > Currently, only x86, alpha and ia64 have implemented architecture
> > specific fast paths. I don't have access to alpha and ia64 systems for
> > testing, but they are legacy systems that are not likely to be updated
> > to the latest kernel anyway.
> >
> > By using a rwsem microbenchmark, the total locking rates on a 4-socket
> > 56-core 112-thread x86-64 system before and after the patch were as
> > follows (mixed means equal # of read and write locks):
> >
> >                       Before Patch              After Patch
> >    # of Threads  wlock   rlock   mixed     wlock   rlock   mixed
> >    ------------  -----   -----   -----     -----   -----   -----
> >         1        27,373  29,409  28,170    28,773  30,164  29,276
> >         2         7,697  14,922   1,703     7,435  15,167   1,729
> >         4         6,987  14,285   1,490     7,181  14,438   1,330
> >         8         6,650  13,652     761     6,918  13,796     718
> >        16         6,434  15,729     713     6,554  16,030     625
> >        32         5,590  15,312     552     6,124  15,344     471
> >        64         5,980  15,478      61     5,668  15,509      58
> >
> > There were some run-to-run variations for the multi-thread tests. For
> > x86-64, using the generic C code fast path seems to be a liitle bit
> > faster than the assembly version especially for read-lock and when lock
> > contention is low.  Looking at the assembly version of the fast paths,
> > there are assembly to/from C code wrappers that save and restore all
> > the callee-clobbered registers (7 registers on x86-64). The assembly
> > generated from the generic C code doesn't need to do that. That may
> > explain the slight performance gain here.
> >
> > The generic asm rwsem.h can also be merged into kernel/locking/rwsem.h
> > as no other code other than those under kernel/locking needs to access
> > the internal rwsem macros and functions.
> >
> > Signed-off-by: Waiman Long <longman@redhat.com>
> 
> I have decided to break the rwsem patchset that I sent out on last
> Thursday into 3 parts. This patch is part 0 as it touches a number of
> arch specific files and so have the widest distribution. I would like to
> get it merged first. Part 1 will be patches 1-10 (except 4) of my
> original rwsem patchset. This part moves things around, adds more
> debugging capability and lays the ground work for the next part. Part 2
> will contains the remaining patches which are the real beef of the whole
> patchset.

Sounds good to me - I've merged this patch, will push it out after 
testing.

Thanks,

	Ingo

^ permalink raw reply	[flat|nested] 13+ messages in thread

* Re: [PATCH] locking/rwsem: Remove arch specific rwsem files
  2019-02-11  2:00 [PATCH] locking/rwsem: Remove arch specific rwsem files Waiman Long
  2019-02-11  2:08 ` Waiman Long
@ 2019-02-11  9:36 ` Peter Zijlstra
  2019-02-11  9:40   ` Peter Zijlstra
  2019-02-11 11:58 ` Peter Zijlstra
  2 siblings, 1 reply; 13+ messages in thread
From: Peter Zijlstra @ 2019-02-11  9:36 UTC (permalink / raw)
  To: Waiman Long
  Cc: Ingo Molnar, Will Deacon, Thomas Gleixner, linux-kernel,
	linux-alpha, linux-arm-kernel, linux-hexagon, linux-ia64,
	linuxppc-dev, linux-sh, sparclinux, linux-xtensa, linux-arch,
	x86, Arnd Bergmann, Borislav Petkov, H. Peter Anvin,
	Davidlohr Bueso, Linus Torvalds, Andrew Morton, Tim Chen

On Sun, Feb 10, 2019 at 09:00:50PM -0500, Waiman Long wrote:
> diff --git a/kernel/locking/rwsem.h b/kernel/locking/rwsem.h
> index bad2bca..067e265 100644
> --- a/kernel/locking/rwsem.h
> +++ b/kernel/locking/rwsem.h
> @@ -32,6 +32,26 @@
>  # define DEBUG_RWSEMS_WARN_ON(c)
>  #endif
>  
> +/*
> + * R/W semaphores originally for PPC using the stuff in lib/rwsem.c.
> + * Adapted largely from include/asm-i386/rwsem.h
> + * by Paul Mackerras <paulus@samba.org>.
> + */
> +
> +/*
> + * the semaphore definition
> + */
> +#ifdef CONFIG_64BIT
> +# define RWSEM_ACTIVE_MASK		0xffffffffL
> +#else
> +# define RWSEM_ACTIVE_MASK		0x0000ffffL
> +#endif
> +
> +#define RWSEM_ACTIVE_BIAS		0x00000001L
> +#define RWSEM_WAITING_BIAS		(-RWSEM_ACTIVE_MASK-1)
> +#define RWSEM_ACTIVE_READ_BIAS		RWSEM_ACTIVE_BIAS
> +#define RWSEM_ACTIVE_WRITE_BIAS		(RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
> +
>  #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
>  /*
>   * All writes to owner are protected by WRITE_ONCE() to make sure that
> @@ -132,3 +152,113 @@ static inline void rwsem_clear_reader_owned(struct rw_semaphore *sem)
>  {
>  }
>  #endif
> +
> +#ifdef CONFIG_RWSEM_XCHGADD_ALGORITHM
> +/*
> + * lock for reading
> + */
> +static inline void __down_read(struct rw_semaphore *sem)
> +{
> +	if (unlikely(atomic_long_inc_return_acquire(&sem->count) <= 0))
> +		rwsem_down_read_failed(sem);
> +}
> +
> +static inline int __down_read_killable(struct rw_semaphore *sem)
> +{
> +	if (unlikely(atomic_long_inc_return_acquire(&sem->count) <= 0)) {
> +		if (IS_ERR(rwsem_down_read_failed_killable(sem)))
> +			return -EINTR;
> +	}
> +
> +	return 0;
> +}
> +
> +static inline int __down_read_trylock(struct rw_semaphore *sem)
> +{
> +	long tmp;
> +
> +	while ((tmp = atomic_long_read(&sem->count)) >= 0) {
> +		if (tmp == atomic_long_cmpxchg_acquire(&sem->count, tmp,
> +				   tmp + RWSEM_ACTIVE_READ_BIAS)) {
> +			return 1;

That really wants to be:

		if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
						    tmp + RWSEM_ACTIVE_READ_BIAS))

> +		}
> +	}
> +	return 0;
> +}
> +
> +/*
> + * lock for writing
> + */
> +static inline void __down_write(struct rw_semaphore *sem)
> +{
> +	long tmp;
> +
> +	tmp = atomic_long_add_return_acquire(RWSEM_ACTIVE_WRITE_BIAS,
> +					     &sem->count);
> +	if (unlikely(tmp != RWSEM_ACTIVE_WRITE_BIAS))
> +		rwsem_down_write_failed(sem);
> +}
> +
> +static inline int __down_write_killable(struct rw_semaphore *sem)
> +{
> +	long tmp;
> +
> +	tmp = atomic_long_add_return_acquire(RWSEM_ACTIVE_WRITE_BIAS,
> +					     &sem->count);
> +	if (unlikely(tmp != RWSEM_ACTIVE_WRITE_BIAS))
> +		if (IS_ERR(rwsem_down_write_failed_killable(sem)))
> +			return -EINTR;
> +	return 0;
> +}
> +
> +static inline int __down_write_trylock(struct rw_semaphore *sem)
> +{
> +	long tmp;

	tmp = RWSEM_UNLOCKED_VALUE;

> +
> +	tmp = atomic_long_cmpxchg_acquire(&sem->count, RWSEM_UNLOCKED_VALUE,
> +		      RWSEM_ACTIVE_WRITE_BIAS);
> +	return tmp == RWSEM_UNLOCKED_VALUE;

	return atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
					       RWSEM_ACTIVE_WRITE_BIAS);

> +}
> +
> +/*
> + * unlock after reading
> + */
> +static inline void __up_read(struct rw_semaphore *sem)
> +{
> +	long tmp;
> +
> +	tmp = atomic_long_dec_return_release(&sem->count);
> +	if (unlikely(tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0))
> +		rwsem_wake(sem);
> +}
> +
> +/*
> + * unlock after writing
> + */
> +static inline void __up_write(struct rw_semaphore *sem)
> +{
> +	if (unlikely(atomic_long_sub_return_release(RWSEM_ACTIVE_WRITE_BIAS,
> +						    &sem->count) < 0))
> +		rwsem_wake(sem);
> +}
> +
> +/*
> + * downgrade write lock to read lock
> + */
> +static inline void __downgrade_write(struct rw_semaphore *sem)
> +{
> +	long tmp;
> +
> +	/*
> +	 * When downgrading from exclusive to shared ownership,
> +	 * anything inside the write-locked region cannot leak
> +	 * into the read side. In contrast, anything in the
> +	 * read-locked region is ok to be re-ordered into the
> +	 * write side. As such, rely on RELEASE semantics.
> +	 */
> +	tmp = atomic_long_add_return_release(-RWSEM_WAITING_BIAS, &sem->count);
> +	if (tmp < 0)
> +		rwsem_downgrade_wake(sem);
> +}
> +
> +#endif /* CONFIG_RWSEM_XCHGADD_ALGORITHM */

^ permalink raw reply	[flat|nested] 13+ messages in thread

* Re: [PATCH] locking/rwsem: Remove arch specific rwsem files
  2019-02-11  9:36 ` Peter Zijlstra
@ 2019-02-11  9:40   ` Peter Zijlstra
  2019-02-11 10:57     ` Peter Zijlstra
  0 siblings, 1 reply; 13+ messages in thread
From: Peter Zijlstra @ 2019-02-11  9:40 UTC (permalink / raw)
  To: Waiman Long
  Cc: Ingo Molnar, Will Deacon, Thomas Gleixner, linux-kernel,
	linux-alpha, linux-arm-kernel, linux-hexagon, linux-ia64,
	linuxppc-dev, linux-sh, sparclinux, linux-xtensa, linux-arch,
	x86, Arnd Bergmann, Borislav Petkov, H. Peter Anvin,
	Davidlohr Bueso, Linus Torvalds, Andrew Morton, Tim Chen

On Mon, Feb 11, 2019 at 10:36:01AM +0100, Peter Zijlstra wrote:
> On Sun, Feb 10, 2019 at 09:00:50PM -0500, Waiman Long wrote:
> > +static inline int __down_read_trylock(struct rw_semaphore *sem)
> > +{
> > +	long tmp;
> > +
> > +	while ((tmp = atomic_long_read(&sem->count)) >= 0) {
> > +		if (tmp == atomic_long_cmpxchg_acquire(&sem->count, tmp,
> > +				   tmp + RWSEM_ACTIVE_READ_BIAS)) {
> > +			return 1;
> 
> That really wants to be:
> 
> 		if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
> 						    tmp + RWSEM_ACTIVE_READ_BIAS))
> 
> > +		}
> > +	}
> > +	return 0;
> > +}

Also, the is the one case where LL/SC can actually do 'better'. Do you
have benchmarks for say PowerPC or ARM64 ?

^ permalink raw reply	[flat|nested] 13+ messages in thread

* Re: [PATCH] locking/rwsem: Remove arch specific rwsem files
  2019-02-11  7:11   ` Ingo Molnar
@ 2019-02-11 10:39     ` Ingo Molnar
  2019-02-11 10:52       ` Will Deacon
  2019-02-11 13:32       ` Waiman Long
  0 siblings, 2 replies; 13+ messages in thread
From: Ingo Molnar @ 2019-02-11 10:39 UTC (permalink / raw)
  To: Waiman Long
  Cc: Peter Zijlstra, Ingo Molnar, Will Deacon, Thomas Gleixner,
	linux-kernel, linux-alpha, linux-arm-kernel, linux-hexagon,
	linux-ia64, linuxppc-dev, linux-sh, sparclinux, linux-xtensa,
	linux-arch, x86, Arnd Bergmann, Borislav Petkov, H. Peter Anvin,
	Davidlohr Bueso, Linus Torvalds, Andrew Morton, Tim Chen


* Ingo Molnar <mingo@kernel.org> wrote:

> Sounds good to me - I've merged this patch, will push it out after 
> testing.

Based on Peter's feedback I'm delaying this - performance testing on at 
least one key ll/sc arch would be nice indeed.

Thanks,

	Ingo

^ permalink raw reply	[flat|nested] 13+ messages in thread

* Re: [PATCH] locking/rwsem: Remove arch specific rwsem files
  2019-02-11 10:39     ` Ingo Molnar
@ 2019-02-11 10:52       ` Will Deacon
  2019-02-11 10:55         ` Ingo Molnar
  2019-02-11 13:32       ` Waiman Long
  1 sibling, 1 reply; 13+ messages in thread
From: Will Deacon @ 2019-02-11 10:52 UTC (permalink / raw)
  To: Ingo Molnar
  Cc: Waiman Long, Peter Zijlstra, Ingo Molnar, Thomas Gleixner,
	linux-kernel, linux-alpha, linux-arm-kernel, linux-hexagon,
	linux-ia64, linuxppc-dev, linux-sh, sparclinux, linux-xtensa,
	linux-arch, x86, Arnd Bergmann, Borislav Petkov, H. Peter Anvin,
	Davidlohr Bueso, Linus Torvalds, Andrew Morton, Tim Chen

On Mon, Feb 11, 2019 at 11:39:27AM +0100, Ingo Molnar wrote:
> 
> * Ingo Molnar <mingo@kernel.org> wrote:
> 
> > Sounds good to me - I've merged this patch, will push it out after 
> > testing.
> 
> Based on Peter's feedback I'm delaying this - performance testing on at 
> least one key ll/sc arch would be nice indeed.

Once Waiman has posted a new version, I can take it for a spin on some
arm64 boxen if he shares his workload.

Will

^ permalink raw reply	[flat|nested] 13+ messages in thread

* Re: [PATCH] locking/rwsem: Remove arch specific rwsem files
  2019-02-11 10:52       ` Will Deacon
@ 2019-02-11 10:55         ` Ingo Molnar
  0 siblings, 0 replies; 13+ messages in thread
From: Ingo Molnar @ 2019-02-11 10:55 UTC (permalink / raw)
  To: Will Deacon
  Cc: Waiman Long, Peter Zijlstra, Ingo Molnar, Thomas Gleixner,
	linux-kernel, linux-alpha, linux-arm-kernel, linux-hexagon,
	linux-ia64, linuxppc-dev, linux-sh, sparclinux, linux-xtensa,
	linux-arch, x86, Arnd Bergmann, Borislav Petkov, H. Peter Anvin,
	Davidlohr Bueso, Linus Torvalds, Andrew Morton, Tim Chen


* Will Deacon <will.deacon@arm.com> wrote:

> On Mon, Feb 11, 2019 at 11:39:27AM +0100, Ingo Molnar wrote:
> > 
> > * Ingo Molnar <mingo@kernel.org> wrote:
> > 
> > > Sounds good to me - I've merged this patch, will push it out after 
> > > testing.
> > 
> > Based on Peter's feedback I'm delaying this - performance testing on at 
> > least one key ll/sc arch would be nice indeed.
> 
> Once Waiman has posted a new version, I can take it for a spin on some
> arm64 boxen if he shares his workload.

Cool, thanks!

	Ingo

^ permalink raw reply	[flat|nested] 13+ messages in thread

* Re: [PATCH] locking/rwsem: Remove arch specific rwsem files
  2019-02-11  9:40   ` Peter Zijlstra
@ 2019-02-11 10:57     ` Peter Zijlstra
  0 siblings, 0 replies; 13+ messages in thread
From: Peter Zijlstra @ 2019-02-11 10:57 UTC (permalink / raw)
  To: Waiman Long
  Cc: Ingo Molnar, Will Deacon, Thomas Gleixner, linux-kernel,
	linux-alpha, linux-arm-kernel, linux-hexagon, linux-ia64,
	linuxppc-dev, linux-sh, sparclinux, linux-xtensa, linux-arch,
	x86, Arnd Bergmann, Borislav Petkov, H. Peter Anvin,
	Davidlohr Bueso, Linus Torvalds, Andrew Morton, Tim Chen

On Mon, Feb 11, 2019 at 10:40:44AM +0100, Peter Zijlstra wrote:
> On Mon, Feb 11, 2019 at 10:36:01AM +0100, Peter Zijlstra wrote:
> > On Sun, Feb 10, 2019 at 09:00:50PM -0500, Waiman Long wrote:
> > > +static inline int __down_read_trylock(struct rw_semaphore *sem)
> > > +{
> > > +	long tmp;
> > > +
> > > +	while ((tmp = atomic_long_read(&sem->count)) >= 0) {
> > > +		if (tmp == atomic_long_cmpxchg_acquire(&sem->count, tmp,
> > > +				   tmp + RWSEM_ACTIVE_READ_BIAS)) {
> > > +			return 1;
> > 
> > That really wants to be:
> > 
> > 		if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
> > 						    tmp + RWSEM_ACTIVE_READ_BIAS))
> > 
> > > +		}
> > > +	}
> > > +	return 0;
> > > +}
> 
> Also, the is the one case where LL/SC can actually do 'better'. Do you
> have benchmarks for say PowerPC or ARM64 ?

Ah, I see they already used asm-generic/rwsem.h which has similar code
to the above.

^ permalink raw reply	[flat|nested] 13+ messages in thread

* Re: [PATCH] locking/rwsem: Remove arch specific rwsem files
  2019-02-11  2:00 [PATCH] locking/rwsem: Remove arch specific rwsem files Waiman Long
  2019-02-11  2:08 ` Waiman Long
  2019-02-11  9:36 ` Peter Zijlstra
@ 2019-02-11 11:58 ` Peter Zijlstra
  2019-02-11 16:35   ` Waiman Long
  2 siblings, 1 reply; 13+ messages in thread
From: Peter Zijlstra @ 2019-02-11 11:58 UTC (permalink / raw)
  To: Waiman Long
  Cc: Ingo Molnar, Will Deacon, Thomas Gleixner, linux-kernel,
	linux-alpha, linux-arm-kernel, linux-hexagon, linux-ia64,
	linuxppc-dev, linux-sh, sparclinux, linux-xtensa, linux-arch,
	x86, Arnd Bergmann, Borislav Petkov, H. Peter Anvin,
	Davidlohr Bueso, Linus Torvalds, Andrew Morton, Tim Chen

[-- Attachment #1: Type: text/plain, Size: 3269 bytes --]

On Sun, Feb 10, 2019 at 09:00:50PM -0500, Waiman Long wrote:

> +static inline int __down_read_trylock(struct rw_semaphore *sem)
> +{
> +	long tmp;
> +
> +	while ((tmp = atomic_long_read(&sem->count)) >= 0) {
> +		if (tmp == atomic_long_cmpxchg_acquire(&sem->count, tmp,
> +				   tmp + RWSEM_ACTIVE_READ_BIAS)) {
> +			return 1;
> +		}
> +	}
> +	return 0;
> +}

So the orignal x86 implementation reads:

  static inline bool __down_read_trylock(struct rw_semaphore *sem)
  {
	  long result, tmp;
	  asm volatile("# beginning __down_read_trylock\n\t"
		       "  mov          %[count],%[result]\n\t"
		       "1:\n\t"
		       "  mov          %[result],%[tmp]\n\t"
		       "  add          %[inc],%[tmp]\n\t"
		       "  jle	     2f\n\t"
		       LOCK_PREFIX "  cmpxchg  %[tmp],%[count]\n\t"
		       "  jnz	     1b\n\t"
		       "2:\n\t"
		       "# ending __down_read_trylock\n\t"
		       : [count] "+m" (sem->count), [result] "=&a" (result),
			 [tmp] "=&r" (tmp)
		       : [inc] "i" (RWSEM_ACTIVE_READ_BIAS)
		       : "memory", "cc");
	  return result >= 0;
  }

you replace that with:

  int __down_read_trylock1(unsigned long *l)
  {
	  long tmp;

	  while ((tmp = READ_ONCE(*l)) >= 0) {
		  if (tmp == cmpxchg(l, tmp, tmp + 1))
			  return 1;
	  }

	  return 0;
  }

which generates:

  0000000000000000 <__down_read_trylock1>:
   0:   eb 17                   jmp    19 <__down_read_trylock1+0x19>
   2:   66 0f 1f 44 00 00       nopw   0x0(%rax,%rax,1)
   8:   48 8d 4a 01             lea    0x1(%rdx),%rcx
   c:   48 89 d0                mov    %rdx,%rax
   f:   f0 48 0f b1 0f          lock cmpxchg %rcx,(%rdi)
  14:   48 39 c2                cmp    %rax,%rdx
  17:   74 0f                   je     28 <__down_read_trylock1+0x28>
  19:   48 8b 17                mov    (%rdi),%rdx
  1c:   48 85 d2                test   %rdx,%rdx
  1f:   79 e7                   jns    8 <__down_read_trylock1+0x8>
  21:   31 c0                   xor    %eax,%eax
  23:   c3                      retq
  24:   0f 1f 40 00             nopl   0x0(%rax)
  28:   b8 01 00 00 00          mov    $0x1,%eax
  2d:   c3                      retq


Which is clearly worse. Now we can write that as:

  int __down_read_trylock2(unsigned long *l)
  {
	  long tmp = READ_ONCE(*l);

	  while (tmp >= 0) {
		  if (try_cmpxchg(l, &tmp, tmp + 1))
			  return 1;
	  }

	  return 0;
  }

which generates:

  0000000000000030 <__down_read_trylock2>:
  30:   48 8b 07                mov    (%rdi),%rax
  33:   48 85 c0                test   %rax,%rax
  36:   78 18                   js     50 <__down_read_trylock2+0x20>
  38:   48 8d 50 01             lea    0x1(%rax),%rdx
  3c:   f0 48 0f b1 17          lock cmpxchg %rdx,(%rdi)
  41:   75 f0                   jne    33 <__down_read_trylock2+0x3>
  43:   b8 01 00 00 00          mov    $0x1,%eax
  48:   c3                      retq
  49:   0f 1f 80 00 00 00 00    nopl   0x0(%rax)
  50:   31 c0                   xor    %eax,%eax
  52:   c3                      retq

Which is a lot better; but not quite there yet.


I've tried quite a bit, but I can't seem to get GCC to generate the:

	add $1,%rdx
	jle

required; stuff like:

	new = old + 1;
	if (new <= 0)

generates:

	lea 0x1(%rax),%rdx
	test %rdx, %rdx
	jle


Ah well, have fun :-)

[-- Attachment #2: dtl.c --]
[-- Type: text/x-csrc, Size: 4530 bytes --]


typedef unsigned char u8;
typedef unsigned short u16;
typedef unsigned int u32;
typedef unsigned long long u64;
typedef signed char s8;
typedef signed short s16;
typedef signed int s32;
typedef signed long long s64;
typedef _Bool bool;

# define CC_SET(c) "\n\t/* output condition code " #c "*/\n"
# define CC_OUT(c) "=@cc" #c

#define likely(x)     __builtin_expect(!!(x), 1)
#define unlikely(x)   __builtin_expect(!!(x), 0)

extern void __cmpxchg_wrong_size(void);

#define __raw_cmpxchg(ptr, old, new, size, lock)			\
({									\
	__typeof__(*(ptr)) __ret;					\
	__typeof__(*(ptr)) __old = (old);				\
	__typeof__(*(ptr)) __new = (new);				\
	switch (size) {							\
	case 1:						\
	{								\
		volatile u8 *__ptr = (volatile u8 *)(ptr);		\
		asm volatile(lock "cmpxchgb %2,%1"			\
			     : "=a" (__ret), "+m" (*__ptr)		\
			     : "q" (__new), "0" (__old)			\
			     : "memory");				\
		break;							\
	}								\
	case 2:						\
	{								\
		volatile u16 *__ptr = (volatile u16 *)(ptr);		\
		asm volatile(lock "cmpxchgw %2,%1"			\
			     : "=a" (__ret), "+m" (*__ptr)		\
			     : "r" (__new), "0" (__old)			\
			     : "memory");				\
		break;							\
	}								\
	case 4:						\
	{								\
		volatile u32 *__ptr = (volatile u32 *)(ptr);		\
		asm volatile(lock "cmpxchgl %2,%1"			\
			     : "=a" (__ret), "+m" (*__ptr)		\
			     : "r" (__new), "0" (__old)			\
			     : "memory");				\
		break;							\
	}								\
	case 8:						\
	{								\
		volatile u64 *__ptr = (volatile u64 *)(ptr);		\
		asm volatile(lock "cmpxchgq %2,%1"			\
			     : "=a" (__ret), "+m" (*__ptr)		\
			     : "r" (__new), "0" (__old)			\
			     : "memory");				\
		break;							\
	}								\
	default:							\
		__cmpxchg_wrong_size();					\
	}								\
	__ret;								\
})

#define __cmpxchg(ptr, old, new, size)					\
	__raw_cmpxchg((ptr), (old), (new), (size), LOCK_PREFIX)

#define cmpxchg(ptr, old, new)						\
	__cmpxchg(ptr, old, new, sizeof(*(ptr)))

#define __raw_try_cmpxchg(_ptr, _pold, _new, size, lock)		\
({									\
	bool success;							\
	__typeof__(_ptr) _old = (__typeof__(_ptr))(_pold);		\
	__typeof__(*(_ptr)) __old = *_old;				\
	__typeof__(*(_ptr)) __new = (_new);				\
	switch (size) {							\
	case 1:						\
	{								\
		volatile u8 *__ptr = (volatile u8 *)(_ptr);		\
		asm volatile(lock "cmpxchgb %[new], %[ptr]"		\
			     CC_SET(z)					\
			     : CC_OUT(z) (success),			\
			       [ptr] "+m" (*__ptr),			\
			       [old] "+a" (__old)			\
			     : [new] "q" (__new)			\
			     : "memory");				\
		break;							\
	}								\
	case 2:						\
	{								\
		volatile u16 *__ptr = (volatile u16 *)(_ptr);		\
		asm volatile(lock "cmpxchgw %[new], %[ptr]"		\
			     CC_SET(z)					\
			     : CC_OUT(z) (success),			\
			       [ptr] "+m" (*__ptr),			\
			       [old] "+a" (__old)			\
			     : [new] "r" (__new)			\
			     : "memory");				\
		break;							\
	}								\
	case 4:						\
	{								\
		volatile u32 *__ptr = (volatile u32 *)(_ptr);		\
		asm volatile(lock "cmpxchgl %[new], %[ptr]"		\
			     CC_SET(z)					\
			     : CC_OUT(z) (success),			\
			       [ptr] "+m" (*__ptr),			\
			       [old] "+a" (__old)			\
			     : [new] "r" (__new)			\
			     : "memory");				\
		break;							\
	}								\
	case 8:						\
	{								\
		volatile u64 *__ptr = (volatile u64 *)(_ptr);		\
		asm volatile(lock "cmpxchgq %[new], %[ptr]"		\
			     CC_SET(z)					\
			     : CC_OUT(z) (success),			\
			       [ptr] "+m" (*__ptr),			\
			       [old] "+a" (__old)			\
			     : [new] "r" (__new)			\
			     : "memory");				\
		break;							\
	}								\
	default:							\
		__cmpxchg_wrong_size();					\
	}								\
	if (unlikely(!success))						\
		*_old = __old;						\
	likely(success);						\
})

#define LOCK_PREFIX "lock; "

#define __try_cmpxchg(ptr, pold, new, size)				\
	__raw_try_cmpxchg((ptr), (pold), (new), (size), LOCK_PREFIX)

#define try_cmpxchg(ptr, pold, new)					\
	__try_cmpxchg((ptr), (pold), (new), sizeof(*(ptr)))

#define READ_ONCE(x) (*(volatile typeof(x) *)(&x))

int __down_read_trylock1(unsigned long *l)
{
	long tmp;

	while ((tmp = READ_ONCE(*l)) >= 0) {
		if (tmp == cmpxchg(l, tmp, tmp + 1))
			return 1;
	}

	return 0;
}

int __down_read_trylock2(unsigned long *l)
{
	long tmp = READ_ONCE(*l);

	while (tmp >= 0) {
		if (try_cmpxchg(l, &tmp, tmp + 1))
			return 1;
	}

	return 0;
}

int __down_read_trylock3(unsigned long *l)
{
	long new, old = READ_ONCE(*l);

	for (;;) {
		new = old + 1;
		if (new <= 0)
			return 0;
		if (try_cmpxchg(l, &old, new))
			return 1;
	}
}


^ permalink raw reply	[flat|nested] 13+ messages in thread

* Re: [PATCH] locking/rwsem: Remove arch specific rwsem files
  2019-02-11 10:39     ` Ingo Molnar
  2019-02-11 10:52       ` Will Deacon
@ 2019-02-11 13:32       ` Waiman Long
  1 sibling, 0 replies; 13+ messages in thread
From: Waiman Long @ 2019-02-11 13:32 UTC (permalink / raw)
  To: Ingo Molnar
  Cc: Peter Zijlstra, Ingo Molnar, Will Deacon, Thomas Gleixner,
	linux-kernel, linux-alpha, linux-arm-kernel, linux-hexagon,
	linux-ia64, linuxppc-dev, linux-sh, sparclinux, linux-xtensa,
	linux-arch, x86, Arnd Bergmann, Borislav Petkov, H. Peter Anvin,
	Davidlohr Bueso, Linus Torvalds, Andrew Morton, Tim Chen

On 02/11/2019 05:39 AM, Ingo Molnar wrote:
> * Ingo Molnar <mingo@kernel.org> wrote:
>
>> Sounds good to me - I've merged this patch, will push it out after 
>> testing.
> Based on Peter's feedback I'm delaying this - performance testing on at 
> least one key ll/sc arch would be nice indeed.
>
> Thanks,
>
> 	Ingo

Yes, I will twist the generic code to generate better code.

As I said in the commit log, only x86, ia64 and alpha provide assembly
code to replace the generic C code. The ll/sc archs that I have access
to (ARM64, ppc) are all using the generic C code anyway. I actually had
done some performance measurement on both those platforms and didn't see
any performance difference. I didn't include them as they were using
generic code before. I will rerun the tests after I twisted the generic
C code.

Thanks,
Longman



^ permalink raw reply	[flat|nested] 13+ messages in thread

* Re: [PATCH] locking/rwsem: Remove arch specific rwsem files
  2019-02-11 11:58 ` Peter Zijlstra
@ 2019-02-11 16:35   ` Waiman Long
  2019-02-11 17:04     ` Peter Zijlstra
  0 siblings, 1 reply; 13+ messages in thread
From: Waiman Long @ 2019-02-11 16:35 UTC (permalink / raw)
  To: Peter Zijlstra
  Cc: Ingo Molnar, Will Deacon, Thomas Gleixner, linux-kernel,
	linux-alpha, linux-arm-kernel, linux-hexagon, linux-ia64,
	linuxppc-dev, linux-sh, sparclinux, linux-xtensa, linux-arch,
	x86, Arnd Bergmann, Borislav Petkov, H. Peter Anvin,
	Davidlohr Bueso, Linus Torvalds, Andrew Morton, Tim Chen

On 02/11/2019 06:58 AM, Peter Zijlstra wrote:
> Which is clearly worse. Now we can write that as:
>
>   int __down_read_trylock2(unsigned long *l)
>   {
> 	  long tmp = READ_ONCE(*l);
>
> 	  while (tmp >= 0) {
> 		  if (try_cmpxchg(l, &tmp, tmp + 1))
> 			  return 1;
> 	  }
>
> 	  return 0;
>   }
>
> which generates:
>
>   0000000000000030 <__down_read_trylock2>:
>   30:   48 8b 07                mov    (%rdi),%rax
>   33:   48 85 c0                test   %rax,%rax
>   36:   78 18                   js     50 <__down_read_trylock2+0x20>
>   38:   48 8d 50 01             lea    0x1(%rax),%rdx
>   3c:   f0 48 0f b1 17          lock cmpxchg %rdx,(%rdi)
>   41:   75 f0                   jne    33 <__down_read_trylock2+0x3>
>   43:   b8 01 00 00 00          mov    $0x1,%eax
>   48:   c3                      retq
>   49:   0f 1f 80 00 00 00 00    nopl   0x0(%rax)
>   50:   31 c0                   xor    %eax,%eax
>   52:   c3                      retq
>
> Which is a lot better; but not quite there yet.
>
>
> I've tried quite a bit, but I can't seem to get GCC to generate the:
>
> 	add $1,%rdx
> 	jle
>
> required; stuff like:
>
> 	new = old + 1;
> 	if (new <= 0)
>
> generates:
>
> 	lea 0x1(%rax),%rdx
> 	test %rdx, %rdx
> 	jle

Thanks for the suggested code snippet. So you want to replace "lea
0x1(%rax), %rdx" by "add $1,%rdx"?

I think the compiler is doing that so as to use the address generation
unit for addition instead of using the ALU. That will leave the ALU
available for doing other arithmetic operation in parallel. I don't
think it is a good idea to override the compiler and force it to use
ALU. So I am not going to try doing that. It is only 1 or 2 more of
codes anyway.

Cheers,
Longman


^ permalink raw reply	[flat|nested] 13+ messages in thread

* Re: [PATCH] locking/rwsem: Remove arch specific rwsem files
  2019-02-11 16:35   ` Waiman Long
@ 2019-02-11 17:04     ` Peter Zijlstra
  0 siblings, 0 replies; 13+ messages in thread
From: Peter Zijlstra @ 2019-02-11 17:04 UTC (permalink / raw)
  To: Waiman Long
  Cc: Ingo Molnar, Will Deacon, Thomas Gleixner, linux-kernel,
	linux-alpha, linux-arm-kernel, linux-hexagon, linux-ia64,
	linuxppc-dev, linux-sh, sparclinux, linux-xtensa, linux-arch,
	x86, Arnd Bergmann, Borislav Petkov, H. Peter Anvin,
	Davidlohr Bueso, Linus Torvalds, Andrew Morton, Tim Chen

On Mon, Feb 11, 2019 at 11:35:24AM -0500, Waiman Long wrote:
> On 02/11/2019 06:58 AM, Peter Zijlstra wrote:
> > Which is clearly worse. Now we can write that as:
> >
> >   int __down_read_trylock2(unsigned long *l)
> >   {
> > 	  long tmp = READ_ONCE(*l);
> >
> > 	  while (tmp >= 0) {
> > 		  if (try_cmpxchg(l, &tmp, tmp + 1))
> > 			  return 1;
> > 	  }
> >
> > 	  return 0;
> >   }
> >
> > which generates:
> >
> >   0000000000000030 <__down_read_trylock2>:
> >   30:   48 8b 07                mov    (%rdi),%rax
> >   33:   48 85 c0                test   %rax,%rax
> >   36:   78 18                   js     50 <__down_read_trylock2+0x20>
> >   38:   48 8d 50 01             lea    0x1(%rax),%rdx
> >   3c:   f0 48 0f b1 17          lock cmpxchg %rdx,(%rdi)
> >   41:   75 f0                   jne    33 <__down_read_trylock2+0x3>
> >   43:   b8 01 00 00 00          mov    $0x1,%eax
> >   48:   c3                      retq
> >   49:   0f 1f 80 00 00 00 00    nopl   0x0(%rax)
> >   50:   31 c0                   xor    %eax,%eax
> >   52:   c3                      retq
> >
> > Which is a lot better; but not quite there yet.
> >
> >
> > I've tried quite a bit, but I can't seem to get GCC to generate the:
> >
> > 	add $1,%rdx
> > 	jle
> >
> > required; stuff like:
> >
> > 	new = old + 1;
> > 	if (new <= 0)
> >
> > generates:
> >
> > 	lea 0x1(%rax),%rdx
> > 	test %rdx, %rdx
> > 	jle
> 
> Thanks for the suggested code snippet. So you want to replace "lea
> 0x1(%rax), %rdx" by "add $1,%rdx"?
> 
> I think the compiler is doing that so as to use the address generation
> unit for addition instead of using the ALU. That will leave the ALU
> available for doing other arithmetic operation in parallel. I don't
> think it is a good idea to override the compiler and force it to use
> ALU. So I am not going to try doing that. It is only 1 or 2 more of
> codes anyway.

Yeah, I was trying to see what I could make it do.. #2 really should be
good enough, but you know how it is once you're poking at it :-)

^ permalink raw reply	[flat|nested] 13+ messages in thread

end of thread, back to index

Thread overview: 13+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-02-11  2:00 [PATCH] locking/rwsem: Remove arch specific rwsem files Waiman Long
2019-02-11  2:08 ` Waiman Long
2019-02-11  7:11   ` Ingo Molnar
2019-02-11 10:39     ` Ingo Molnar
2019-02-11 10:52       ` Will Deacon
2019-02-11 10:55         ` Ingo Molnar
2019-02-11 13:32       ` Waiman Long
2019-02-11  9:36 ` Peter Zijlstra
2019-02-11  9:40   ` Peter Zijlstra
2019-02-11 10:57     ` Peter Zijlstra
2019-02-11 11:58 ` Peter Zijlstra
2019-02-11 16:35   ` Waiman Long
2019-02-11 17:04     ` Peter Zijlstra

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