[patch 0/7] Immediate Values (redux) for 2.6.24-rc4-git3

[patch 0/7] Immediate Values (redux) for 2.6.24-rc4-git3

[Mathieu Desnoyers]

Hi,

Here are the redux version of immediate values. It currently supports x86_32,
x86_64 and powerpc. The other architectures use a generic fallback (a simple
variable).

It depends on the text edit lock patches. It diminishes the impact of dormant
markers by providing a fast branch over a function call with a "load immediate"
instruction. It minimizes the d-cache hit.

This redux version it not reentrant wrt NMIs and MCEs. One must be cautious not
to use it in code paths reached by such execution contexts.

It could be interesting to queue this for 2.6.25.

Mathieu

-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68

[patch 1/7] Immediate Values - Architecture Independent Code

[Mathieu Desnoyers]

[-- Attachment #1: immediate-values-architecture-independent-code.patch --]
[-- Type: text/plain, Size: 18558 bytes --]

Immediate values are used as read mostly variables that are rarely updated. They
use code patching to modify the values inscribed in the instruction stream. It
provides a way to save precious cache lines that would otherwise have to be used
by these variables.

There is a generic _imv_read() version, which uses standard global
variables, and optimized per architecture imv_read() implementations,
which use a load immediate to remove a data cache hit. When the immediate values
functionnality is disabled in the kernel, it falls back to global variables.

It adds a new rodata section "__imv" to place the pointers to the enable
value. Immediate values activation functions sits in kernel/immediate.c.

Immediate values refer to the memory address of a previously declared integer.
This integer holds the information about the state of the immediate values
associated, and must be accessed through the API found in linux/immediate.h.

At module load time, each immediate value is checked to see if it must be
enabled. It would be the case if the variable they refer to is exported from
another module and already enabled.

In the early stages of start_kernel(), the immediate values are updated to
reflect the state of the variable they refer to.

* Why should this be merged *

It improves performances on heavy memory I/O workloads.

An interesting result shows the potential this infrastructure has by
showing the slowdown a simple system call such as getppid() suffers when it is
used under heavy user-space cache trashing:

Random walk L1 and L2 trashing surrounding a getppid() call:
(note: in this test, do_syscal_trace was taken at each system call, see
Documentation/immediate.txt in these patches for details)
- No memory pressure :   getppid() takes  1573 cycles
- With memory pressure : getppid() takes 15589 cycles

We therefore have a slowdown of 10 times just to get the kernel variables from
memory. Another test on the same architecture (Intel P4) measured the memory
latency to be 559 cycles. Therefore, each cache line removed from the hot path
would improve the syscall time of 3.5% in these conditions.

Changelog:

- section __imv is already SHF_ALLOC
- Because of the wonders of ELF, section 0 has sh_addr and sh_size 0.  So
  the if (immediateindex) is unnecessary here.
- Remove module_mutex usage: depend on functions implemented in module.c for
  that.
- Does not update tainted module's immediate values.
- remove imv_*_t types, add DECLARE_IMV() and DEFINE_IMV().
  - imv_read(&var) becomes imv_read(var) because of this.
- Adding a new EXPORT_IMV_SYMBOL(_GPL).
- remove imv_if(). Should use if (unlikely(imv_read(var))) instead.
  - Wait until we have gcc support before we add the imv_if macro, since
    its form may have to change.
- Dont't declare the __imv section in vmlinux.lds.h, just put the content
  in the rodata section.
- Simplify interface : remove imv_set_early, keep track of kernel boot
  status internally.
- Remove the ALIGN(8) before the __imv section. It is packed now.
- Uses an IPI busy-loop on each CPU with interrupts disabled as a simple,
  architecture agnostic, update mechanism.
- Use imv_* instead of immediate_*.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
CC: Rusty Russell <rusty@rustcorp.com.au>
---
 include/asm-generic/vmlinux.lds.h |    3 
 include/linux/immediate.h         |   94 +++++++++++++++++++
 include/linux/module.h            |   16 +++
 init/main.c                       |    8 +
 kernel/Makefile                   |    1 
 kernel/immediate.c                |  187 ++++++++++++++++++++++++++++++++++++++
 kernel/module.c                   |   50 +++++++++-
 7 files changed, 358 insertions(+), 1 deletion(-)

Index: linux-2.6-lttng/include/linux/immediate.h
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6-lttng/include/linux/immediate.h	2007-11-28 09:32:04.000000000 -0500
@@ -0,0 +1,94 @@
+#ifndef _LINUX_IMMEDIATE_H
+#define _LINUX_IMMEDIATE_H
+
+/*
+ * Immediate values, can be updated at runtime and save cache lines.
+ *
+ * (C) Copyright 2007 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
+ *
+ * This file is released under the GPLv2.
+ * See the file COPYING for more details.
+ */
+
+#ifdef CONFIG_IMMEDIATE
+
+struct __imv {
+	unsigned long var;	/* Pointer to the identifier variable of the
+				 * immediate value
+				 */
+	unsigned long imv;	/*
+				 * Pointer to the memory location of the
+				 * immediate value within the instruction.
+				 */
+	unsigned char size;	/* Type size. */
+} __attribute__ ((packed));
+
+#include <asm/immediate.h>
+
+/**
+ * imv_set - set immediate variable (with locking)
+ * @name: immediate value name
+ * @i: required value
+ *
+ * Sets the value of @name, taking the module_mutex if required by
+ * the architecture.
+ */
+#define imv_set(name, i)						\
+	do {								\
+		name##__imv = (i);					\
+		core_imv_update();					\
+		module_imv_update();					\
+	} while (0)
+
+/*
+ * Internal update functions.
+ */
+extern void core_imv_update(void);
+extern void imv_update_range(const struct __imv *begin,
+	const struct __imv *end);
+
+#else
+
+/*
+ * Generic immediate values: a simple, standard, memory load.
+ */
+
+/**
+ * imv_read - read immediate variable
+ * @name: immediate value name
+ *
+ * Reads the value of @name.
+ */
+#define imv_read(name)			_imv_read(name)
+
+/**
+ * imv_set - set immediate variable (with locking)
+ * @name: immediate value name
+ * @i: required value
+ *
+ * Sets the value of @name, taking the module_mutex if required by
+ * the architecture.
+ */
+#define imv_set(name, i)		(name##__imv = (i))
+
+static inline void core_imv_update(void) { }
+static inline void module_imv_update(void) { }
+
+#endif
+
+#define DECLARE_IMV(type, name) extern __typeof__(type) name##__imv
+#define DEFINE_IMV(type, name)  __typeof__(type) name##__imv
+
+#define EXPORT_IMV_SYMBOL(name) EXPORT_SYMBOL(name##__imv)
+#define EXPORT_IMV_SYMBOL_GPL(name) EXPORT_SYMBOL_GPL(name##__imv)
+
+/**
+ * _imv_read - Read immediate value with standard memory load.
+ * @name: immediate value name
+ *
+ * Force a data read of the immediate value instead of the immediate value
+ * based mechanism. Useful for __init and __exit section data read.
+ */
+#define _imv_read(name)		(name##__imv)
+
+#endif
Index: linux-2.6-lttng/include/linux/module.h
===================================================================
--- linux-2.6-lttng.orig/include/linux/module.h	2007-11-28 09:31:51.000000000 -0500
+++ linux-2.6-lttng/include/linux/module.h	2007-11-28 09:32:04.000000000 -0500
@@ -15,6 +15,7 @@
 #include <linux/stringify.h>
 #include <linux/kobject.h>
 #include <linux/moduleparam.h>
+#include <linux/immediate.h>
 #include <linux/marker.h>
 #include <asm/local.h>
 
@@ -355,6 +356,10 @@ struct module
 	/* The command line arguments (may be mangled).  People like
 	   keeping pointers to this stuff */
 	char *args;
+#ifdef CONFIG_IMMEDIATE
+	const struct __imv *immediate;
+	unsigned int num_immediate;
+#endif
 #ifdef CONFIG_MARKERS
 	struct marker *markers;
 	unsigned int num_markers;
@@ -464,6 +469,9 @@ extern void print_modules(void);
 
 extern void module_update_markers(void);
 
+extern void _module_imv_update(void);
+extern void module_imv_update(void);
+
 #else /* !CONFIG_MODULES... */
 #define EXPORT_SYMBOL(sym)
 #define EXPORT_SYMBOL_GPL(sym)
@@ -568,6 +576,14 @@ static inline void module_update_markers
 {
 }
 
+static inline void _module_imv_update(void)
+{
+}
+
+static inline void module_imv_update(void)
+{
+}
+
 #endif /* CONFIG_MODULES */
 
 struct device_driver;
Index: linux-2.6-lttng/kernel/module.c
===================================================================
--- linux-2.6-lttng.orig/kernel/module.c	2007-11-28 09:31:51.000000000 -0500
+++ linux-2.6-lttng/kernel/module.c	2007-11-28 09:32:04.000000000 -0500
@@ -33,6 +33,7 @@
 #include <linux/cpu.h>
 #include <linux/moduleparam.h>
 #include <linux/errno.h>
+#include <linux/immediate.h>
 #include <linux/err.h>
 #include <linux/vermagic.h>
 #include <linux/notifier.h>
@@ -1675,6 +1676,7 @@ static struct module *load_module(void _
 	unsigned int unusedcrcindex;
 	unsigned int unusedgplindex;
 	unsigned int unusedgplcrcindex;
+	unsigned int immediateindex;
 	unsigned int markersindex;
 	unsigned int markersstringsindex;
 	struct module *mod;
@@ -1773,6 +1775,7 @@ static struct module *load_module(void _
 #ifdef ARCH_UNWIND_SECTION_NAME
 	unwindex = find_sec(hdr, sechdrs, secstrings, ARCH_UNWIND_SECTION_NAME);
 #endif
+	immediateindex = find_sec(hdr, sechdrs, secstrings, "__imv");
 
 	/* Don't keep modinfo section */
 	sechdrs[infoindex].sh_flags &= ~(unsigned long)SHF_ALLOC;
@@ -1924,6 +1927,11 @@ static struct module *load_module(void _
 	mod->gpl_future_syms = (void *)sechdrs[gplfutureindex].sh_addr;
 	if (gplfuturecrcindex)
 		mod->gpl_future_crcs = (void *)sechdrs[gplfuturecrcindex].sh_addr;
+#ifdef CONFIG_IMMEDIATE
+	mod->immediate = (void *)sechdrs[immediateindex].sh_addr;
+	mod->num_immediate =
+		sechdrs[immediateindex].sh_size / sizeof(*mod->immediate);
+#endif
 
 	mod->unused_syms = (void *)sechdrs[unusedindex].sh_addr;
 	if (unusedcrcindex)
@@ -1991,11 +1999,16 @@ static struct module *load_module(void _
 
 	add_kallsyms(mod, sechdrs, symindex, strindex, secstrings);
 
+	if (!mod->taints) {
 #ifdef CONFIG_MARKERS
-	if (!mod->taints)
 		marker_update_probe_range(mod->markers,
 			mod->markers + mod->num_markers);
 #endif
+#ifdef CONFIG_IMMEDIATE
+		imv_update_range(mod->immediate,
+			mod->immediate + mod->num_immediate);
+#endif
+	}
 	err = module_finalize(hdr, sechdrs, mod);
 	if (err < 0)
 		goto cleanup;
@@ -2601,3 +2614,38 @@ void module_update_markers(void)
 	mutex_unlock(&module_mutex);
 }
 #endif
+
+#ifdef CONFIG_IMMEDIATE
+/**
+ * _module_imv_update - update all immediate values in the kernel
+ *
+ * Iterate on the kernel core and modules to update the immediate values.
+ * Module_mutex must be held be the caller.
+ */
+void _module_imv_update(void)
+{
+	struct module *mod;
+
+	list_for_each_entry(mod, &modules, list) {
+		if (mod->taints)
+			continue;
+		imv_update_range(mod->immediate,
+			mod->immediate + mod->num_immediate);
+	}
+}
+EXPORT_SYMBOL_GPL(_module_imv_update);
+
+/**
+ * module_imv_update - update all immediate values in the kernel
+ *
+ * Iterate on the kernel core and modules to update the immediate values.
+ * Takes module_mutex.
+ */
+void module_imv_update(void)
+{
+	mutex_lock(&module_mutex);
+	_module_imv_update();
+	mutex_unlock(&module_mutex);
+}
+EXPORT_SYMBOL_GPL(module_imv_update);
+#endif
Index: linux-2.6-lttng/kernel/immediate.c
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6-lttng/kernel/immediate.c	2007-11-28 09:32:04.000000000 -0500
@@ -0,0 +1,187 @@
+/*
+ * Copyright (C) 2007 Mathieu Desnoyers
+ *
+ * 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.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ */
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/immediate.h>
+#include <linux/memory.h>
+#include <linux/cpu.h>
+
+#include <asm/cacheflush.h>
+
+/*
+ * Kernel ready to execute the SMP update that may depend on trap and ipi.
+ */
+static int imv_early_boot_complete;
+
+extern const struct __imv __start___imv[];
+extern const struct __imv __stop___imv[];
+
+/*
+ * imv_mutex nests inside module_mutex. imv_mutex protects builtin
+ * immediates and module immediates.
+ */
+static DEFINE_MUTEX(imv_mutex);
+
+static atomic_t wait_sync;
+
+struct ipi_loop_data {
+	long value;
+	const struct __imv *imv;
+} loop_data;
+
+static void ipi_busy_loop(void *arg)
+{
+	unsigned long flags;
+
+	local_irq_save(flags);
+	atomic_dec(&wait_sync);
+	do {
+		/* Make sure the wait_sync gets re-read */
+		smp_mb();
+	} while (atomic_read(&wait_sync) > loop_data.value);
+	atomic_dec(&wait_sync);
+	do {
+		/* Make sure the wait_sync gets re-read */
+		smp_mb();
+	} while (atomic_read(&wait_sync) > 0);
+	/*
+	 * Issuing a synchronizing instruction must be done on each CPU before
+	 * reenabling interrupts after modifying an instruction. Required by
+	 * Intel's errata.
+	 */
+	sync_core();
+	flush_icache_range(loop_data.imv->imv,
+		loop_data.imv->imv + loop_data.imv->size);
+	local_irq_restore(flags);
+}
+
+/**
+ * apply_imv_update - update one immediate value
+ * @imv: pointer of type const struct __imv to update
+ *
+ * Update one immediate value. Must be called with imv_mutex held.
+ * It makes sure all CPUs are not executing the modified code by having them
+ * busy looping with interrupts disabled.
+ * It does _not_ protect against NMI and MCE (could be a problem with Intel's
+ * errata if we use immediate values in their code path).
+ */
+static int apply_imv_update(const struct __imv *imv)
+{
+	unsigned long flags;
+	long online_cpus;
+
+	/*
+	 * If the variable and the instruction have the same value, there is
+	 * nothing to do.
+	 */
+	switch (imv->size) {
+	case 1:	if (*(uint8_t *)imv->imv
+				== *(uint8_t *)imv->var)
+			return 0;
+		break;
+	case 2:	if (*(uint16_t *)imv->imv
+				== *(uint16_t *)imv->var)
+			return 0;
+		break;
+	case 4:	if (*(uint32_t *)imv->imv
+				== *(uint32_t *)imv->var)
+			return 0;
+		break;
+	case 8:	if (*(uint64_t *)imv->imv
+				== *(uint64_t *)imv->var)
+			return 0;
+		break;
+	default:return -EINVAL;
+	}
+
+	if (imv_early_boot_complete) {
+		kernel_text_lock();
+		lock_cpu_hotplug();
+		online_cpus = num_online_cpus();
+		atomic_set(&wait_sync, 2 * online_cpus);
+		loop_data.value = online_cpus;
+		loop_data.imv = imv;
+		smp_call_function(ipi_busy_loop, NULL, 1, 0);
+		local_irq_save(flags);
+		atomic_dec(&wait_sync);
+		do {
+			/* Make sure the wait_sync gets re-read */
+			smp_mb();
+		} while (atomic_read(&wait_sync) > online_cpus);
+		text_poke((void *)imv->imv, (void *)imv->var,
+				imv->size);
+		/*
+		 * Make sure the modified instruction is seen by all CPUs before
+		 * we continue (visible to other CPUs and local interrupts).
+		 */
+		wmb();
+		atomic_dec(&wait_sync);
+		flush_icache_range(imv->imv,
+				imv->imv + imv->size);
+		local_irq_restore(flags);
+		unlock_cpu_hotplug();
+		kernel_text_unlock();
+	} else
+		text_poke_early((void *)imv->imv, (void *)imv->var,
+				imv->size);
+	return 0;
+}
+
+/**
+ * imv_update_range - Update immediate values in a range
+ * @begin: pointer to the beginning of the range
+ * @end: pointer to the end of the range
+ *
+ * Updates a range of immediates.
+ */
+void imv_update_range(const struct __imv *begin,
+		const struct __imv *end)
+{
+	const struct __imv *iter;
+	int ret;
+	for (iter = begin; iter < end; iter++) {
+		mutex_lock(&imv_mutex);
+		ret = apply_imv_update(iter);
+		if (imv_early_boot_complete && ret)
+			printk(KERN_WARNING
+				"Invalid immediate value. "
+				"Variable at %p, "
+				"instruction at %p, size %hu\n",
+				(void *)iter->imv,
+				(void *)iter->var, iter->size);
+		mutex_unlock(&imv_mutex);
+	}
+}
+EXPORT_SYMBOL_GPL(imv_update_range);
+
+/**
+ * imv_update - update all immediate values in the kernel
+ *
+ * Iterate on the kernel core and modules to update the immediate values.
+ */
+void core_imv_update(void)
+{
+	/* Core kernel imvs */
+	imv_update_range(__start___imv, __stop___imv);
+}
+EXPORT_SYMBOL_GPL(core_imv_update);
+
+void __init imv_init_complete(void)
+{
+	imv_early_boot_complete = 1;
+}
Index: linux-2.6-lttng/init/main.c
===================================================================
--- linux-2.6-lttng.orig/init/main.c	2007-11-28 09:27:34.000000000 -0500
+++ linux-2.6-lttng/init/main.c	2007-11-28 09:32:04.000000000 -0500
@@ -57,6 +57,7 @@
 #include <linux/device.h>
 #include <linux/kthread.h>
 #include <linux/sched.h>
+#include <linux/immediate.h>
 
 #include <asm/io.h>
 #include <asm/bugs.h>
@@ -101,6 +102,11 @@ static inline void mark_rodata_ro(void) 
 #ifdef CONFIG_TC
 extern void tc_init(void);
 #endif
+#ifdef CONFIG_IMMEDIATE
+extern void imv_init_complete(void);
+#else
+static inline void imv_init_complete(void) { }
+#endif
 
 enum system_states system_state;
 EXPORT_SYMBOL(system_state);
@@ -518,6 +524,7 @@ asmlinkage void __init start_kernel(void
 	unwind_init();
 	lockdep_init();
 	cgroup_init_early();
+	core_imv_update();
 
 	local_irq_disable();
 	early_boot_irqs_off();
@@ -639,6 +646,7 @@ asmlinkage void __init start_kernel(void
 	cpuset_init();
 	taskstats_init_early();
 	delayacct_init();
+	imv_init_complete();
 
 	check_bugs();
 
Index: linux-2.6-lttng/kernel/Makefile
===================================================================
--- linux-2.6-lttng.orig/kernel/Makefile	2007-11-28 09:27:34.000000000 -0500
+++ linux-2.6-lttng/kernel/Makefile	2007-11-28 09:32:04.000000000 -0500
@@ -56,6 +56,7 @@ obj-$(CONFIG_RELAY) += relay.o
 obj-$(CONFIG_SYSCTL) += utsname_sysctl.o
 obj-$(CONFIG_TASK_DELAY_ACCT) += delayacct.o
 obj-$(CONFIG_TASKSTATS) += taskstats.o tsacct.o
+obj-$(CONFIG_IMMEDIATE) += immediate.o
 obj-$(CONFIG_MARKERS) += marker.o
 
 ifneq ($(CONFIG_SCHED_NO_NO_OMIT_FRAME_POINTER),y)
Index: linux-2.6-lttng/include/asm-generic/vmlinux.lds.h
===================================================================
--- linux-2.6-lttng.orig/include/asm-generic/vmlinux.lds.h	2007-11-28 09:27:34.000000000 -0500
+++ linux-2.6-lttng/include/asm-generic/vmlinux.lds.h	2007-11-28 09:32:04.000000000 -0500
@@ -25,6 +25,9 @@
 		*(.rodata) *(.rodata.*)					\
 		*(__vermagic)		/* Kernel version magic */	\
 		*(__markers_strings)	/* Markers: strings */		\
+		VMLINUX_SYMBOL(__start___imv) = .;			\
+		*(__imv)		/* Immediate values: pointers */ \
+		VMLINUX_SYMBOL(__stop___imv) = .;			\
 	}								\
 									\
 	.rodata1          : AT(ADDR(.rodata1) - LOAD_OFFSET) {		\

-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68

[patch 2/7] Immediate Values - Kconfig menu in EMBEDDED

[Mathieu Desnoyers]

[-- Attachment #1: immediate-values-kconfig-embedded.patch --]
[-- Type: text/plain, Size: 2663 bytes --]

Immediate values provide a way to use dynamic code patching to update variables
sitting within the instruction stream. It saves caches lines normally used by
static read mostly variables. Enable it by default, but let users disable it
through the EMBEDDED menu with the "Disable immediate values" submenu entry.

Note: Since I think that I really should let embedded systems developers using
RO memory the option to disable the immediate values, I choose to leave this
menu option there, in the EMBEDDED menu. Also, the "CONFIG_IMMEDIATE" makes
sense because we want to compile out all the immediate code when we decide not
to use optimized immediate values at all (it removes otherwise unused code).

Changelog:
- Change ARCH_SUPPORTS_IMMEDIATE for ARCH_HAS_IMMEDIATE

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
CC: Rusty Russell <rusty@rustcorp.com.au>
CC: Adrian Bunk <bunk@stusta.de>
CC: Andi Kleen <andi@firstfloor.org>
CC: Alexey Dobriyan <adobriyan@gmail.com>
CC: Christoph Hellwig <hch@infradead.org>
---
 init/Kconfig |   24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

Index: linux-2.6-lttng/init/Kconfig
===================================================================
--- linux-2.6-lttng.orig/init/Kconfig	2007-12-05 20:53:19.000000000 -0500
+++ linux-2.6-lttng/init/Kconfig	2007-12-05 20:53:35.000000000 -0500
@@ -435,6 +435,20 @@ config CC_OPTIMIZE_FOR_SIZE
 config SYSCTL
 	bool
 
+config IMMEDIATE
+	default y if !DISABLE_IMMEDIATE
+	depends on HAVE_IMMEDIATE
+	bool
+	help
+	  Immediate values are used as read-mostly variables that are rarely
+	  updated. They use code patching to modify the values inscribed in the
+	  instruction stream. It provides a way to save precious cache lines
+	  that would otherwise have to be used by these variables. They can be
+	  disabled through the EMBEDDED menu.
+
+config HAVE_IMMEDIATE
+	def_bool n
+
 menuconfig EMBEDDED
 	bool "Configure standard kernel features (for small systems)"
 	help
@@ -670,6 +684,16 @@ config MARKERS
 
 source "arch/Kconfig"
 
+config DISABLE_IMMEDIATE
+	default y if EMBEDDED
+	bool "Disable immediate values" if EMBEDDED
+	depends on HAVE_IMMEDIATE
+	help
+	  Disable code patching based immediate values for embedded systems. It
+	  consumes slightly more memory and requires to modify the instruction
+	  stream each time a variable is updated. Should really be disabled for
+	  embedded systems with read-only text.
+
 endmenu		# General setup
 
 config RT_MUTEXES

-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68

[patch 3/7] x86: add <asm/asm.h>

[Mathieu Desnoyers]

[-- Attachment #1: add-x86-asm-asm-h.patch --]
[-- Type: text/plain, Size: 786 bytes --]

x86: add <asm/asm.h>

Create <asm/asm.h>, with common definitions suitable for assembly
unification.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
---

diff --git a/include/asm-x86/asm.h b/include/asm-x86/asm.h
new file mode 100644
index 0000000..b5006eb
--- /dev/null
+++ b/include/asm-x86/asm.h
@@ -0,0 +1,18 @@
+#ifndef _ASM_X86_ASM_H
+#define _ASM_X86_ASM_H
+
+#ifdef CONFIG_X86_32
+/* 32 bits */
+
+# define _ASM_PTR	" .long "
+# define _ASM_ALIGN	" .balign 4 "
+
+#else
+/* 64 bits */
+
+# define _ASM_PTR	" .quad "
+# define _ASM_ALIGN	" .balign 8 "
+
+#endif /* CONFIG_X86_32 */
+
+#endif /* _ASM_X86_ASM_H */

-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68

[patch 4/7] Immediate Values - x86 Optimization

[Mathieu Desnoyers]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: immediate-values-x86-optimization.patch --]
[-- Type: text/plain, Size: 5288 bytes --]

x86 optimization of the immediate values which uses a movl with code patching
to set/unset the value used to populate the register used as variable source.

Changelog:
- Use text_poke_early with cr0 WP save/restore to patch the bypass. We are doing
  non atomic writes to a code region only touched by us (nobody can execute it
  since we are protected by the imv_mutex).
- Put imv_set and _imv_set in the architecture independent header.
- Use $0 instead of %2 with (0) operand.
- Add x86_64 support, ready for i386+x86_64 -> x86 merge.
- Use asm-x86/asm.h.

Ok, so the most flexible solution that I see, that should fit for both
i386 and x86_64 would be :
1 byte  : "=Q" : Any register accessible as rh: a, b, c, and d.
2, 4 bytes : "=R" : Legacy register—the eight integer registers available
                 on all i386 processors (a, b, c, d, si, di, bp, sp). 8
bytes : (only for x86_64)
          "=r" : A register operand is allowed provided that it is in a
                 general register.
That should make sure x86_64 won't try to use REX prefixed opcodes for
1, 2 and 4 bytes values.

- Create the instruction in a discarded section to calculate its size. This is
  how we can align the beginning of the instruction on an address that will
  permit atomic modificatino of the immediate value without knowing the size of
  the opcode used by the compiler.
- Bugfix : 8 bytes 64 bits immediate value was declared as "4 bytes" in the
  immediate structure.
- Change the immediate.c update code to support variable length opcodes.

- Vastly simplified, using a busy looping IPI with interrupts disabled.
  Does not protect against NMI nor MCE.
- Pack the __imv section. Use smallest types required for size (char).
- Use imv_* instead of immediate_*.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
CC: Andi Kleen <ak@muc.de>
CC: "H. Peter Anvin" <hpa@zytor.com>
CC: Chuck Ebbert <cebbert@redhat.com>
CC: Christoph Hellwig <hch@infradead.org>
CC: Jeremy Fitzhardinge <jeremy@goop.org>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: Ingo Molnar <mingo@redhat.com>
CC: Rusty Russell <rusty@rustcorp.com.au>
---
 arch/x86/Kconfig            |    1 
 include/asm-x86/immediate.h |   77 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 78 insertions(+)

Index: linux-2.6-lttng/include/asm-x86/immediate.h
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6-lttng/include/asm-x86/immediate.h	2007-11-21 11:04:33.000000000 -0500
@@ -0,0 +1,77 @@
+#ifndef _ASM_X86_IMMEDIATE_H
+#define _ASM_X86_IMMEDIATE_H
+
+/*
+ * Immediate values. x86 architecture optimizations.
+ *
+ * (C) Copyright 2006 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
+ *
+ * This file is released under the GPLv2.
+ * See the file COPYING for more details.
+ */
+
+#include <asm/asm.h>
+
+/**
+ * imv_read - read immediate variable
+ * @name: immediate value name
+ *
+ * Reads the value of @name.
+ * Optimized version of the immediate.
+ * Do not use in __init and __exit functions. Use _imv_read() instead.
+ * If size is bigger than the architecture long size, fall back on a memory
+ * read.
+ *
+ * Make sure to populate the initial static 64 bits opcode with a value
+ * what will generate an instruction with 8 bytes immediate value (not the REX.W
+ * prefixed one that loads a sign extended 32 bits immediate value in a r64
+ * register).
+ */
+#define imv_read(name)							\
+	({								\
+		__typeof__(name##__imv) value;				\
+		BUILD_BUG_ON(sizeof(value) > 8);			\
+		switch (sizeof(value)) {				\
+		case 1:							\
+			asm(".section __imv,\"a\",@progbits\n\t"	\
+				_ASM_PTR "%c1, (3f)-%c2\n\t"		\
+				".byte %c2\n\t"				\
+				".previous\n\t"				\
+				"mov $0,%0\n\t"				\
+				"3:\n\t"				\
+				: "=q" (value)				\
+				: "i" (&name##__imv),			\
+				  "i" (sizeof(value)));			\
+			break;						\
+		case 2:							\
+		case 4:							\
+			asm(".section __imv,\"a\",@progbits\n\t"	\
+				_ASM_PTR "%c1, (3f)-%c2\n\t"		\
+				".byte %c2\n\t"				\
+				".previous\n\t"				\
+				"mov $0,%0\n\t"				\
+				"3:\n\t"				\
+				: "=r" (value)				\
+				: "i" (&name##__imv),			\
+				  "i" (sizeof(value)));			\
+			break;						\
+		case 8:							\
+			if (sizeof(long) < 8) {				\
+				value = name##__imv;			\
+				break;					\
+			}						\
+			asm(".section __imv,\"a\",@progbits\n\t"	\
+				_ASM_PTR "%c1, (3f)-%c2\n\t"		\
+				".byte %c2\n\t"				\
+				".previous\n\t"				\
+				"mov $0xFEFEFEFE01010101,%0\n\t" 	\
+				"3:\n\t"				\
+				: "=r" (value)				\
+				: "i" (&name##__imv),			\
+				  "i" (sizeof(value)));			\
+			break;						\
+		};							\
+		value;							\
+	})
+
+#endif /* _ASM_X86_IMMEDIATE_H */
Index: linux-2.6-lttng/arch/x86/Kconfig
===================================================================
--- linux-2.6-lttng.orig/arch/x86/Kconfig	2007-11-21 11:04:06.000000000 -0500
+++ linux-2.6-lttng/arch/x86/Kconfig	2007-11-21 11:04:33.000000000 -0500
@@ -21,6 +21,7 @@ config X86
 	default y
 	select HAVE_OPROFILE
 	select HAVE_KPROBES
+	select HAVE_IMMEDIATE
 
 config GENERIC_TIME
 	bool

-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68

[patch 5/7] Add text_poke and sync_core to powerpc

[Mathieu Desnoyers]

[-- Attachment #1: add-text-poke-to-powerpc.patch --]
[-- Type: text/plain, Size: 1355 bytes --]

- Needed on architectures where we must surround live instruction modification
  with "WP flag disable".
- Turns into a memcpy on powerpc since there is no WP flag activated for
  instruction pages (yet..).
- Add empty sync_core to powerpc so it can be used in architecture independent
  code.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
CC: Rusty Russell <rusty@rustcorp.com.au>
CC: Christoph Hellwig <hch@infradead.org>
CC: Paul Mackerras <paulus@samba.org>
---
 include/asm-powerpc/cacheflush.h |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

Index: linux-2.6-lttng/include/asm-powerpc/cacheflush.h
===================================================================
--- linux-2.6-lttng.orig/include/asm-powerpc/cacheflush.h	2007-11-19 12:05:50.000000000 -0500
+++ linux-2.6-lttng/include/asm-powerpc/cacheflush.h	2007-11-19 13:27:36.000000000 -0500
@@ -63,7 +63,9 @@ extern void flush_dcache_phys_range(unsi
 #define copy_from_user_page(vma, page, vaddr, dst, src, len) \
 	memcpy(dst, src, len)
 
-
+#define text_poke	memcpy
+#define text_poke_early	text_poke
+#define sync_core()
 
 #ifdef CONFIG_DEBUG_PAGEALLOC
 /* internal debugging function */

-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68

[patch 6/7] Immediate Values - Powerpc Optimization

[Mathieu Desnoyers]

[-- Attachment #1: immediate-values-powerpc-optimization.patch --]
[-- Type: text/plain, Size: 3003 bytes --]

PowerPC optimization of the immediate values which uses a li instruction,
patched with an immediate value.

Changelog:
- Put imv_set and _imv_set in the architecture independent header.
- Pack the __imv section. Use smallest types required for size (char).
- Remove architecture specific update code : now handled by architecture
  agnostic code.
- Use imv_* instead of immediate_*.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
CC: Rusty Russell <rusty@rustcorp.com.au>
CC: Christoph Hellwig <hch@infradead.org>
CC: Paul Mackerras <paulus@samba.org>
---
 arch/powerpc/Kconfig            |    1 
 include/asm-powerpc/immediate.h |   55 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 56 insertions(+)

Index: linux-2.6-lttng/include/asm-powerpc/immediate.h
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6-lttng/include/asm-powerpc/immediate.h	2007-11-19 12:26:16.000000000 -0500
@@ -0,0 +1,55 @@
+#ifndef _ASM_POWERPC_IMMEDIATE_H
+#define _ASM_POWERPC_IMMEDIATE_H
+
+/*
+ * Immediate values. PowerPC architecture optimizations.
+ *
+ * (C) Copyright 2006 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
+ *
+ * This file is released under the GPLv2.
+ * See the file COPYING for more details.
+ */
+
+#include <asm/asm-compat.h>
+
+/**
+ * imv_read - read immediate variable
+ * @name: immediate value name
+ *
+ * Reads the value of @name.
+ * Optimized version of the immediate.
+ * Do not use in __init and __exit functions. Use _imv_read() instead.
+ */
+#define imv_read(name)							\
+	({								\
+		__typeof__(name##__imv) value;				\
+		BUILD_BUG_ON(sizeof(value) > 8);			\
+		switch (sizeof(value)) {				\
+		case 1:							\
+			asm(".section __imv,\"a\",@progbits\n\t"	\
+					PPC_LONG "%c1, ((1f)-1)\n\t"	\
+					".byte 1\n\t"			\
+					".previous\n\t"			\
+					"li %0,0\n\t"			\
+					"1:\n\t"			\
+				: "=r" (value)				\
+				: "i" (&name##__imv));			\
+			break;						\
+		case 2:							\
+			asm(".section __imv,\"a\",@progbits\n\t"	\
+					PPC_LONG "%c1, ((1f)-2)\n\t"	\
+					".byte 2\n\t"			\
+					".previous\n\t"			\
+					"li %0,0\n\t"			\
+					"1:\n\t"			\
+				: "=r" (value)				\
+				: "i" (&name##__imv));			\
+			break;						\
+		case 4:							\
+		case 8:	value = name##__imv;				\
+			break;						\
+		};							\
+		value;							\
+	})
+
+#endif /* _ASM_POWERPC_IMMEDIATE_H */
Index: linux-2.6-lttng/arch/powerpc/Kconfig
===================================================================
--- linux-2.6-lttng.orig/arch/powerpc/Kconfig	2007-11-19 12:25:21.000000000 -0500
+++ linux-2.6-lttng/arch/powerpc/Kconfig	2007-11-19 12:26:01.000000000 -0500
@@ -81,6 +81,7 @@ config PPC
 	default y
 	select HAVE_OPROFILE
 	select HAVE_KPROBES
+	select HAVE_IMMEDIATE
 
 config EARLY_PRINTK
 	bool

-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68

[patch 7/7] Immediate Values - Documentation

[Mathieu Desnoyers]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: immediate-values-documentation.patch --]
[-- Type: text/plain, Size: 8867 bytes --]

Changelog:
- Remove imv_set_early (removed from API).
- Use imv_* instead of immediate_*.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
CC: Rusty Russell <rusty@rustcorp.com.au>
---
 Documentation/immediate.txt |  221 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 221 insertions(+)

Index: linux-2.6-lttng/Documentation/immediate.txt
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6-lttng/Documentation/immediate.txt	2007-11-03 20:28:58.000000000 -0400
@@ -0,0 +1,221 @@
+		        Using the Immediate Values
+
+			    Mathieu Desnoyers
+
+
+This document introduces Immediate Values and their use.
+
+
+* Purpose of immediate values
+
+An immediate value is used to compile into the kernel variables that sit within
+the instruction stream. They are meant to be rarely updated but read often.
+Using immediate values for these variables will save cache lines.
+
+This infrastructure is specialized in supporting dynamic patching of the values
+in the instruction stream when multiple CPUs are running without disturbing the
+normal system behavior.
+
+Compiling code meant to be rarely enabled at runtime can be done using
+if (unlikely(imv_read(var))) as condition surrounding the code. The
+smallest data type required for the test (an 8 bits char) is preferred, since
+some architectures, such as powerpc, only allow up to 16 bits immediate values.
+
+
+* Usage
+
+In order to use the "immediate" macros, you should include linux/immediate.h.
+
+#include <linux/immediate.h>
+
+DEFINE_IMV(char, this_immediate);
+EXPORT_IMV_SYMBOL(this_immediate);
+
+
+And use, in the body of a function:
+
+Use imv_set(this_immediate) to set the immediate value.
+
+Use imv_read(this_immediate) to read the immediate value.
+
+The immediate mechanism supports inserting multiple instances of the same
+immediate. Immediate values can be put in inline functions, inlined static
+functions, and unrolled loops.
+
+If you have to read the immediate values from a function declared as __init or
+__exit, you should explicitly use _imv_read(), which will fall back on a
+global variable read. Failing to do so will leave a reference to the __init
+section after it is freed (it would generate a modpost warning).
+
+You can choose to set an initial static value to the immediate by using, for
+instance:
+
+DEFINE_IMV(long, myptr) = 10;
+
+
+* Optimization for a given architecture
+
+One can implement optimized immediate values for a given architecture by
+replacing asm-$ARCH/immediate.h.
+
+
+* Performance improvement
+
+
+  * Memory hit for a data-based branch
+
+Here are the results on a 3GHz Pentium 4:
+
+number of tests: 100
+number of branches per test: 100000
+memory hit cycles per iteration (mean): 636.611
+L1 cache hit cycles per iteration (mean): 89.6413
+instruction stream based test, cycles per iteration (mean): 85.3438
+Just getting the pointer from a modulo on a pseudo-random value, doing
+  nothing with it, cycles per iteration (mean): 77.5044
+
+So:
+Base case:                      77.50 cycles
+instruction stream based test:  +7.8394 cycles
+L1 cache hit based test:        +12.1369 cycles
+Memory load based test:         +559.1066 cycles
+
+So let's say we have a ping flood coming at
+(14014 packets transmitted, 14014 received, 0% packet loss, time 1826ms)
+7674 packets per second. If we put 2 markers for irq entry/exit, it
+brings us to 15348 markers sites executed per second.
+
+(15348 exec/s) * (559 cycles/exec) / (3G cycles/s) = 0.0029
+We therefore have a 0.29% slowdown just on this case.
+
+Compared to this, the instruction stream based test will cause a
+slowdown of:
+
+(15348 exec/s) * (7.84 cycles/exec) / (3G cycles/s) = 0.00004
+For a 0.004% slowdown.
+
+If we plan to use this for memory allocation, spinlock, and all sorts of
+very high event rate tracing, we can assume it will execute 10 to 100
+times more sites per second, which brings us to 0.4% slowdown with the
+instruction stream based test compared to 29% slowdown with the memory
+load based test on a system with high memory pressure.
+
+
+
+  * Markers impact under heavy memory load
+
+Running a kernel with my LTTng instrumentation set, in a test that
+generates memory pressure (from userspace) by trashing L1 and L2 caches
+between calls to getppid() (note: syscall_trace is active and calls
+a marker upon syscall entry and syscall exit; markers are disarmed).
+This test is done in user-space, so there are some delays due to IRQs
+coming and to the scheduler. (UP 2.6.22-rc6-mm1 kernel, task with -20
+nice level)
+
+My first set of results: Linear cache trashing, turned out not to be
+very interesting, because it seems like the linearity of the memset on a
+full array is somehow detected and it does not "really" trash the
+caches.
+
+Now the most interesting result: Random walk L1 and L2 trashing
+surrounding a getppid() call.
+
+- Markers compiled out (but syscall_trace execution forced)
+number of tests: 10000
+No memory pressure
+Reading timestamps takes 108.033 cycles
+getppid: 1681.4 cycles
+With memory pressure
+Reading timestamps takes 102.938 cycles
+getppid: 15691.6 cycles
+
+
+- With the immediate values based markers:
+number of tests: 10000
+No memory pressure
+Reading timestamps takes 108.006 cycles
+getppid: 1681.84 cycles
+With memory pressure
+Reading timestamps takes 100.291 cycles
+getppid: 11793 cycles
+
+
+- With global variables based markers:
+number of tests: 10000
+No memory pressure
+Reading timestamps takes 107.999 cycles
+getppid: 1669.06 cycles
+With memory pressure
+Reading timestamps takes 102.839 cycles
+getppid: 12535 cycles
+
+The result is quite interesting in that the kernel is slower without
+markers than with markers. I explain it by the fact that the data
+accessed is not laid out in the same manner in the cache lines when the
+markers are compiled in or out. It seems that it aligns the function's
+data better to compile-in the markers in this case.
+
+But since the interesting comparison is between the immediate values and
+global variables based markers, and because they share the same memory
+layout, except for the movl being replaced by a movz, we see that the
+global variable based markers (2 markers) adds 742 cycles to each system
+call (syscall entry and exit are traced and memory locations for both
+global variables lie on the same cache line).
+
+
+- Test redone with less iterations, but with error estimates
+
+10 runs of 100 iterations each: Tests done on a 3GHz P4. Here I run getppid with
+syscall trace inactive, comparing the case with memory pressure and without
+memory pressure. (sorry, my system is not setup to execute syscall_trace this
+time, but it will make the point anyway).
+
+No memory pressure
+Reading timestamps:     150.92 cycles,     std dev.    1.01 cycles
+getppid:               1462.09 cycles,     std dev.   18.87 cycles
+
+With memory pressure
+Reading timestamps:     578.22 cycles,     std dev.  269.51 cycles
+getppid:              17113.33 cycles,     std dev. 1655.92 cycles
+
+
+Now for memory read timing: (10 runs, branches per test: 100000)
+Memory read based branch:
+                       644.09 cycles,      std dev.   11.39 cycles
+L1 cache hit based branch:
+                        88.16 cycles,      std dev.    1.35 cycles
+
+
+So, now that we have the raw results, let's calculate:
+
+Memory read:
+644.09±11.39 - 88.16±1.35 = 555.93±11.46 cycles
+
+Getppid without memory pressure:
+1462.09±18.87 - 150.92±1.01 = 1311.17±18.90 cycles
+
+Getppid with memory pressure:
+17113.33±1655.92 - 578.22±269.51 = 16535.11±1677.71 cycles
+
+Therefore, if we add 2 markers not based on immediate values to the getppid
+code, which would add 2 memory reads, we would add
+2 * 555.93±12.74 = 1111.86±25.48 cycles
+
+Therefore,
+
+1111.86±25.48 / 16535.11±1677.71 = 0.0672
+ relative error: sqrt(((25.48/1111.86)^2)+((1677.71/16535.11)^2))
+                     = 0.1040
+ absolute error: 0.1040 * 0.0672 = 0.0070
+
+Therefore: 0.0672±0.0070 * 100% = 6.72±0.70 %
+
+We can therefore affirm that adding 2 markers to getppid, on a system with high
+memory pressure, would have a performance hit of at least 6.0% on the system
+call time, all within the uncertainty limits of these tests. The same applies to
+other kernel code paths. The smaller those code paths are, the highest the
+impact ratio will be.
+
+Therefore, not only is it interesting to use the immediate values to dynamically
+activate dormant code such as the markers, but I think it should also be
+considered as a replacement for many of the "read-mostly" static variables.

-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68