From: tip-bot for Waiman Long <tipbot@zytor.com>
To: linux-tip-commits@vger.kernel.org
Cc: torvalds@linux-foundation.org, riel@redhat.com,
Waiman.Long@hp.com, boris.ostrovsky@oracle.com,
paolo.bonzini@gmail.com, mingo@kernel.org, hpa@zytor.com,
oleg@redhat.com, daniel@numascale.com,
paulmck@linux.vnet.ibm.com, david.vrabel@citrix.com,
tglx@linutronix.de, konrad.wilk@oracle.com, bp@alien8.de,
doug.hatch@hp.com, linux-kernel@vger.kernel.org,
raghavendra.kt@linux.vnet.ibm.com, peterz@infradead.org,
scott.norton@hp.com, akpm@linux-foundation.org
Subject: [tip:locking/core] locking/qspinlock: Extract out code snippets for the next patch
Date: Fri, 8 May 2015 06:26:29 -0700 [thread overview]
Message-ID: <tip-6403bd7d0ea1878a487296114eccf78658d7dd7a@git.kernel.org> (raw)
In-Reply-To: <1429901803-29771-5-git-send-email-Waiman.Long@hp.com>
Commit-ID: 6403bd7d0ea1878a487296114eccf78658d7dd7a
Gitweb: http://git.kernel.org/tip/6403bd7d0ea1878a487296114eccf78658d7dd7a
Author: Waiman Long <Waiman.Long@hp.com>
AuthorDate: Fri, 24 Apr 2015 14:56:33 -0400
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Fri, 8 May 2015 12:36:41 +0200
locking/qspinlock: Extract out code snippets for the next patch
This is a preparatory patch that extracts out the following 2 code
snippets to prepare for the next performance optimization patch.
1) the logic for the exchange of new and previous tail code words
into a new xchg_tail() function.
2) the logic for clearing the pending bit and setting the locked bit
into a new clear_pending_set_locked() function.
This patch also simplifies the trylock operation before queuing by
calling queued_spin_trylock() directly.
Signed-off-by: Waiman Long <Waiman.Long@hp.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Daniel J Blueman <daniel@numascale.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Douglas Hatch <doug.hatch@hp.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paolo Bonzini <paolo.bonzini@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Scott J Norton <scott.norton@hp.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: virtualization@lists.linux-foundation.org
Cc: xen-devel@lists.xenproject.org
Link: http://lkml.kernel.org/r/1429901803-29771-5-git-send-email-Waiman.Long@hp.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
include/asm-generic/qspinlock_types.h | 2 +
kernel/locking/qspinlock.c | 79 +++++++++++++++++++++--------------
2 files changed, 50 insertions(+), 31 deletions(-)
diff --git a/include/asm-generic/qspinlock_types.h b/include/asm-generic/qspinlock_types.h
index 7ee6632..3a7f671 100644
--- a/include/asm-generic/qspinlock_types.h
+++ b/include/asm-generic/qspinlock_types.h
@@ -58,6 +58,8 @@ typedef struct qspinlock {
#define _Q_TAIL_CPU_BITS (32 - _Q_TAIL_CPU_OFFSET)
#define _Q_TAIL_CPU_MASK _Q_SET_MASK(TAIL_CPU)
+#define _Q_TAIL_MASK (_Q_TAIL_IDX_MASK | _Q_TAIL_CPU_MASK)
+
#define _Q_LOCKED_VAL (1U << _Q_LOCKED_OFFSET)
#define _Q_PENDING_VAL (1U << _Q_PENDING_OFFSET)
diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c
index af9c2ef..82bb4a9 100644
--- a/kernel/locking/qspinlock.c
+++ b/kernel/locking/qspinlock.c
@@ -97,6 +97,42 @@ static inline struct mcs_spinlock *decode_tail(u32 tail)
#define _Q_LOCKED_PENDING_MASK (_Q_LOCKED_MASK | _Q_PENDING_MASK)
/**
+ * clear_pending_set_locked - take ownership and clear the pending bit.
+ * @lock: Pointer to queued spinlock structure
+ *
+ * *,1,0 -> *,0,1
+ */
+static __always_inline void clear_pending_set_locked(struct qspinlock *lock)
+{
+ atomic_add(-_Q_PENDING_VAL + _Q_LOCKED_VAL, &lock->val);
+}
+
+/**
+ * xchg_tail - Put in the new queue tail code word & retrieve previous one
+ * @lock : Pointer to queued spinlock structure
+ * @tail : The new queue tail code word
+ * Return: The previous queue tail code word
+ *
+ * xchg(lock, tail)
+ *
+ * p,*,* -> n,*,* ; prev = xchg(lock, node)
+ */
+static __always_inline u32 xchg_tail(struct qspinlock *lock, u32 tail)
+{
+ u32 old, new, val = atomic_read(&lock->val);
+
+ for (;;) {
+ new = (val & _Q_LOCKED_PENDING_MASK) | tail;
+ old = atomic_cmpxchg(&lock->val, val, new);
+ if (old == val)
+ break;
+
+ val = old;
+ }
+ return old;
+}
+
+/**
* queued_spin_lock_slowpath - acquire the queued spinlock
* @lock: Pointer to queued spinlock structure
* @val: Current value of the queued spinlock 32-bit word
@@ -178,15 +214,7 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
*
* *,1,0 -> *,0,1
*/
- for (;;) {
- new = (val & ~_Q_PENDING_MASK) | _Q_LOCKED_VAL;
-
- old = atomic_cmpxchg(&lock->val, val, new);
- if (old == val)
- break;
-
- val = old;
- }
+ clear_pending_set_locked(lock);
return;
/*
@@ -203,37 +231,26 @@ queue:
node->next = NULL;
/*
- * We have already touched the queueing cacheline; don't bother with
- * pending stuff.
- *
- * trylock || xchg(lock, node)
- *
- * 0,0,0 -> 0,0,1 ; no tail, not locked -> no tail, locked.
- * p,y,x -> n,y,x ; tail was p -> tail is n; preserving locked.
+ * We touched a (possibly) cold cacheline in the per-cpu queue node;
+ * attempt the trylock once more in the hope someone let go while we
+ * weren't watching.
*/
- for (;;) {
- new = _Q_LOCKED_VAL;
- if (val)
- new = tail | (val & _Q_LOCKED_PENDING_MASK);
-
- old = atomic_cmpxchg(&lock->val, val, new);
- if (old == val)
- break;
-
- val = old;
- }
+ if (queued_spin_trylock(lock))
+ goto release;
/*
- * we won the trylock; forget about queueing.
+ * We have already touched the queueing cacheline; don't bother with
+ * pending stuff.
+ *
+ * p,*,* -> n,*,*
*/
- if (new == _Q_LOCKED_VAL)
- goto release;
+ old = xchg_tail(lock, tail);
/*
* if there was a previous node; link it and wait until reaching the
* head of the waitqueue.
*/
- if (old & ~_Q_LOCKED_PENDING_MASK) {
+ if (old & _Q_TAIL_MASK) {
prev = decode_tail(old);
WRITE_ONCE(prev->next, node);
next prev parent reply other threads:[~2015-05-08 13:28 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-24 18:56 [PATCH v16 00/14] qspinlock: a 4-byte queue spinlock with PV support Waiman Long
2015-04-24 18:56 ` [PATCH v16 01/14] qspinlock: A simple generic 4-byte queue spinlock Waiman Long
2015-05-08 13:25 ` [tip:locking/core] locking/qspinlock: Introduce a simple generic 4-byte queued spinlock tip-bot for Waiman Long
2015-04-24 18:56 ` [PATCH v16 02/14] qspinlock, x86: Enable x86-64 to use queue spinlock Waiman Long
2015-05-08 13:25 ` [tip:locking/core] locking/qspinlock, x86: Enable x86-64 to use queued spinlocks tip-bot for Waiman Long
2015-04-24 18:56 ` [PATCH v16 03/14] qspinlock: Add pending bit Waiman Long
2015-05-08 13:26 ` [tip:locking/core] locking/qspinlock: " tip-bot for Peter Zijlstra (Intel)
2015-04-24 18:56 ` [PATCH v16 04/14] qspinlock: Extract out code snippets for the next patch Waiman Long
2015-05-08 13:26 ` tip-bot for Waiman Long [this message]
2015-04-24 18:56 ` [PATCH v16 05/14] qspinlock: Optimize for smaller NR_CPUS Waiman Long
2015-05-08 13:26 ` [tip:locking/core] locking/qspinlock: " tip-bot for Peter Zijlstra (Intel)
2015-04-24 18:56 ` [PATCH v16 06/14] qspinlock: Use a simple write to grab the lock Waiman Long
2015-05-08 13:27 ` [tip:locking/core] locking/qspinlock: " tip-bot for Waiman Long
2015-04-24 18:56 ` [PATCH v16 07/14] qspinlock: Revert to test-and-set on hypervisors Waiman Long
2015-05-08 13:27 ` [tip:locking/core] locking/qspinlock: " tip-bot for Peter Zijlstra (Intel)
2015-04-24 18:56 ` [PATCH v16 08/14] pvqspinlock: Implement simple paravirt support for the qspinlock Waiman Long
2015-05-04 14:20 ` Peter Zijlstra
2015-05-04 17:15 ` Waiman Long
2015-05-08 13:27 ` [tip:locking/core] locking/pvqspinlock: " tip-bot for Waiman Long
2015-04-24 18:56 ` [PATCH v16 09/14] pvqspinlock, x86: Implement the paravirt qspinlock call patching Waiman Long
2015-05-08 13:27 ` [tip:locking/core] locking/pvqspinlock, " tip-bot for Peter Zijlstra (Intel)
2015-05-30 4:09 ` Sasha Levin
2015-05-31 18:29 ` Waiman Long
2015-04-24 18:56 ` [PATCH v16 10/14] pvqspinlock, x86: Enable PV qspinlock for KVM Waiman Long
2015-05-08 13:28 ` [tip:locking/core] locking/pvqspinlock, " tip-bot for Waiman Long
2015-04-24 18:56 ` [PATCH v16 11/14] pvqspinlock, x86: Enable PV qspinlock for Xen Waiman Long
2015-05-08 13:28 ` [tip:locking/core] locking/pvqspinlock, " tip-bot for David Vrabel
2015-04-24 18:56 ` [PATCH v16 12/14] pvqspinlock: Only kick CPU at unlock time Waiman Long
2015-04-24 18:56 ` [PATCH v16 13/14] pvqspinlock: Improve slowpath performance by avoiding cmpxchg Waiman Long
2015-04-29 18:11 ` Peter Zijlstra
2015-04-29 18:27 ` Linus Torvalds
2015-04-30 18:56 ` Waiman Long
2015-04-30 18:49 ` Waiman Long
2015-05-04 14:05 ` Peter Zijlstra
2015-05-04 17:18 ` Waiman Long
2015-04-24 18:56 ` [PATCH v16 14/14] pvqspinlock: Collect slowpath lock statistics Waiman Long
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=tip-6403bd7d0ea1878a487296114eccf78658d7dd7a@git.kernel.org \
--to=tipbot@zytor.com \
--cc=Waiman.Long@hp.com \
--cc=akpm@linux-foundation.org \
--cc=boris.ostrovsky@oracle.com \
--cc=bp@alien8.de \
--cc=daniel@numascale.com \
--cc=david.vrabel@citrix.com \
--cc=doug.hatch@hp.com \
--cc=hpa@zytor.com \
--cc=konrad.wilk@oracle.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-tip-commits@vger.kernel.org \
--cc=mingo@kernel.org \
--cc=oleg@redhat.com \
--cc=paolo.bonzini@gmail.com \
--cc=paulmck@linux.vnet.ibm.com \
--cc=peterz@infradead.org \
--cc=raghavendra.kt@linux.vnet.ibm.com \
--cc=riel@redhat.com \
--cc=scott.norton@hp.com \
--cc=tglx@linutronix.de \
--cc=torvalds@linux-foundation.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).