[rfc-patch 0/9] Immediate Values for 2.6.24-rc2-git5

[rfc-patch 0/9] Immediate Values for 2.6.24-rc2-git5

[Mathieu Desnoyers]

Here are the updated immediate values following comments. The main changes :

- Declares a packed __immediate section to use less space. Declare the "size" as
  a char instead of an int.
- Simplified x86 immediate values update, spinning with IRQs disabled instead of
  using an lockless update algorithm. Is is simpler, but won't support NMI or
  MCE code updates.

This is submitted for another round of comments.

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

[rfc-patch 1/9] Immediate Values - Architecture Independent Code

[Mathieu Desnoyers]

[-- Attachment #1: immediate-values-architecture-independent-code.patch --]
[-- Type: text/plain, Size: 16699 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 _immediate_read() version, which uses standard global
variables, and optimized per architecture immediate_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 "__immediate" 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 __immediate 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 immediate_*_t types, add DECLARE_IMMEDIATE() and DEFINE_IMMEDIATE().
  - immediate_read(&var) becomes immediate_read(var) because of this.
- Adding a new EXPORT_IMMEDIATE_SYMBOL(_GPL).
- remove immediate_if(). Should use if (unlikely(immediate_read(var))) instead.
  - Wait until we have gcc support before we add the immediate_if macro, since
    its form may have to change.
- Document immediate_set_early(). This design is chosen over immediate_init()
  because:
    - We can mark the function __init so it is freed after boot.
    - Module code patching can also be done by the "normal" function. This is
      preferred, even if it can be slightly slower, because update performance
      does not matter.
    - immediate_init() could confuse users because we can actually "initialize"
      an immediate value to a certain value, which will be used as initial
      value. e.g.:
        static DEFINE_IMMEDIATE(int, var) = 10;
- Dont't declare the __immediate section in vmlinux.lds.h, just put the content
  in the rodata section.
- Simplify interface : remove immediate_set_early, keep track of kernel boot
  status internally.
- Remove the ALIGN(8) before the __immediate section. It is packed now.

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         |   83 ++++++++++++++++++++++++++++++++++++
 include/linux/module.h            |   16 +++++++
 init/main.c                       |    8 +++
 kernel/Makefile                   |    1 
 kernel/immediate.c                |   86 ++++++++++++++++++++++++++++++++++++++
 kernel/module.c                   |   50 +++++++++++++++++++++-
 7 files changed, 246 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	2007-11-15 23:26:14.000000000 -0500
@@ -0,0 +1,83 @@
+#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
+
+#include <asm/immediate.h>
+
+/**
+ * immediate_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 immediate_set(name, i)						\
+	do {								\
+		name##__immediate = (i);				\
+		core_immediate_update();				\
+		module_immediate_update();				\
+	} while (0)
+
+/*
+ * Internal update functions.
+ */
+extern void core_immediate_update(void);
+extern void immediate_update_range(const struct __immediate *begin,
+	const struct __immediate *end);
+
+#else
+
+/*
+ * Generic immediate values: a simple, standard, memory load.
+ */
+
+/**
+ * immediate_read - read immediate variable
+ * @name: immediate value name
+ *
+ * Reads the value of @name.
+ */
+#define immediate_read(name)		_immediate_read(name)
+
+/**
+ * immediate_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 immediate_set(name, i)		(name##__immediate = (i))
+
+static inline void core_immediate_update(void) { }
+static inline void module_immediate_update(void) { }
+
+#endif
+
+#define DECLARE_IMMEDIATE(type, name) extern __typeof__(type) name##__immediate
+#define DEFINE_IMMEDIATE(type, name)  __typeof__(type) name##__immediate
+
+#define EXPORT_IMMEDIATE_SYMBOL(name) EXPORT_SYMBOL(name##__immediate)
+#define EXPORT_IMMEDIATE_SYMBOL_GPL(name) EXPORT_SYMBOL_GPL(name##__immediate)
+
+/**
+ * _immediate_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 _immediate_read(name)		(name##__immediate)
+
+#endif
Index: linux-2.6-lttng/include/linux/module.h
===================================================================
--- linux-2.6-lttng.orig/include/linux/module.h	2007-11-15 23:25:57.000000000 -0500
+++ linux-2.6-lttng/include/linux/module.h	2007-11-16 11:37:43.000000000 -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 __immediate *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(struct module *probe_module, int *refcount);
 
+extern void _module_immediate_update(void);
+extern void module_immediate_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_immediate_update(void)
+{
+}
+
+static inline void module_immediate_update(void)
+{
+}
+
 #endif /* CONFIG_MODULES */
 
 struct device_driver;
Index: linux-2.6-lttng/kernel/module.c
===================================================================
--- linux-2.6-lttng.orig/kernel/module.c	2007-11-15 23:25:57.000000000 -0500
+++ linux-2.6-lttng/kernel/module.c	2007-11-16 11:37:44.000000000 -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>
@@ -1673,6 +1674,7 @@ 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;
@@ -1771,6 +1773,7 @@ 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, "__immediate");
 
 	/* Don't keep modinfo section */
 	sechdrs[infoindex].sh_flags &= ~(unsigned long)SHF_ALLOC;
@@ -1922,6 +1925,11 @@ 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)
@@ -1989,11 +1997,16 @@ 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, NULL, NULL);
 #endif
+#ifdef CONFIG_IMMEDIATE
+		immediate_update_range(mod->immediate,
+			mod->immediate + mod->num_immediate);
+#endif
+	}
 	err = module_finalize(hdr, sechdrs, mod);
 	if (err < 0)
 		goto cleanup;
@@ -2600,3 +2613,38 @@ void module_update_markers(struct module
 	mutex_unlock(&module_mutex);
 }
 #endif
+
+#ifdef CONFIG_IMMEDIATE
+/**
+ * _module_immediate_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_immediate_update(void)
+{
+	struct module *mod;
+
+	list_for_each_entry(mod, &modules, list) {
+		if (mod->taints)
+			continue;
+		immediate_update_range(mod->immediate,
+			mod->immediate + mod->num_immediate);
+	}
+}
+EXPORT_SYMBOL_GPL(_module_immediate_update);
+
+/**
+ * module_immediate_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_immediate_update(void)
+{
+	mutex_lock(&module_mutex);
+	_module_immediate_update();
+	mutex_unlock(&module_mutex);
+}
+EXPORT_SYMBOL_GPL(module_immediate_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	2007-11-16 11:37:32.000000000 -0500
@@ -0,0 +1,86 @@
+/*
+ * 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>
+
+/*
+ * Kernel ready to execute the SMP update that may depend on trap and ipi.
+ */
+static int immediate_early_boot_complete;
+
+extern const struct __immediate __start___immediate[];
+extern const struct __immediate __stop___immediate[];
+
+/*
+ * immediate_mutex nests inside module_mutex. immediate_mutex protects builtin
+ * immediates and module immediates.
+ */
+static DEFINE_MUTEX(immediate_mutex);
+
+/**
+ * immediate_update_range - Update immediate values in a range
+ * @begin: pointer to the beginning of the range
+ * @end: pointer to the end of the range
+ *
+ * Sets a range of immediates to a enabled state : set the enable bit.
+ */
+void immediate_update_range(const struct __immediate *begin,
+		const struct __immediate *end)
+{
+	const struct __immediate *iter;
+	int ret;
+	if (immediate_early_boot_complete) {
+		for (iter = begin; iter < end; iter++) {
+			mutex_lock(&immediate_mutex);
+			kernel_text_lock();
+			ret = arch_immediate_update(iter);
+			kernel_text_unlock();
+			if (ret)
+				printk(KERN_WARNING
+					"Invalid immediate value. "
+					"Variable at %p, "
+					"instruction at %p, size %hu\n",
+					(void *)iter->immediate,
+					(void *)iter->var, iter->size);
+			mutex_unlock(&immediate_mutex);
+		}
+	} else
+		for (iter = begin; iter < end; iter++)
+			arch_immediate_update_early(iter);
+}
+EXPORT_SYMBOL_GPL(immediate_update_range);
+
+/**
+ * immediate_update - update all immediate values in the kernel
+ * @lock: should a module_mutex be taken ?
+ *
+ * Iterate on the kernel core and modules to update the immediate values.
+ */
+void core_immediate_update(void)
+{
+	/* Core kernel immediates */
+	immediate_update_range(__start___immediate, __stop___immediate);
+}
+EXPORT_SYMBOL_GPL(core_immediate_update);
+
+void __init immediate_init_complete(void)
+{
+	immediate_early_boot_complete = 1;
+}
Index: linux-2.6-lttng/init/main.c
===================================================================
--- linux-2.6-lttng.orig/init/main.c	2007-11-15 23:25:57.000000000 -0500
+++ linux-2.6-lttng/init/main.c	2007-11-15 23:26:14.000000000 -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 immediate_init_complete(void);
+#else
+static inline void immediate_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_immediate_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();
+	immediate_init_complete();
 
 	check_bugs();
 
Index: linux-2.6-lttng/kernel/Makefile
===================================================================
--- linux-2.6-lttng.orig/kernel/Makefile	2007-11-15 23:25:57.000000000 -0500
+++ linux-2.6-lttng/kernel/Makefile	2007-11-15 23:26:14.000000000 -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	2007-11-15 23:25:57.000000000 -0500
+++ linux-2.6-lttng/include/asm-generic/vmlinux.lds.h	2007-11-16 11:04:35.000000000 -0500
@@ -25,6 +25,9 @@
 		*(.rodata) *(.rodata.*)					\
 		*(__vermagic)		/* Kernel version magic */	\
 		*(__markers_strings)	/* Markers: strings */		\
+		VMLINUX_SYMBOL(__start___immediate) = .;		\
+		*(__immediate)		/* Immediate values: pointers */ \
+		VMLINUX_SYMBOL(__stop___immediate) = .;			\
 	}								\
 									\
 	.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

[rfc-patch 2/9] Immediate Values - Kconfig menu in EMBEDDED

[Mathieu Desnoyers]

[-- Attachment #1: immediate-values-kconfig-embedded.patch --]
[-- Type: text/plain, Size: 2621 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: 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	2007-11-15 22:18:42.000000000 -0500
+++ linux-2.6-lttng/init/Kconfig	2007-11-15 22:19:24.000000000 -0500
@@ -428,6 +428,20 @@ 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
@@ -663,6 +677,16 @@ 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

[rfc-patch 3/9] Immediate Values - Move Kprobes x86 restore_interrupt to kdebug.h

[Mathieu Desnoyers]

[-- Attachment #1: immediate-values-move-kprobes-x86-restore-interrupt-to-kdebug-h.patch --]
[-- Type: text/plain, Size: 3383 bytes --]

Since the breakpoint handler is useful both to kprobes and immediate values, it
makes sense to make the required restore_interrupt() available through
asm-i386/kdebug.h.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Acked-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
CC: Christoph Hellwig <hch@infradead.org>
CC: prasanna@in.ibm.com
CC: anil.s.keshavamurthy@intel.com
CC: davem@davemloft.net
CC: Thomas Gleixner <tglx@linutronix.de>
CC: Ingo Molnar <mingo@redhat.com>
CC: H. Peter Anvin <hpa@zytor.com>
---
 include/asm-x86/kdebug.h     |   12 ++++++++++++
 include/asm-x86/kprobes_32.h |    9 ---------
 include/asm-x86/kprobes_64.h |    9 ---------
 3 files changed, 12 insertions(+), 18 deletions(-)

Index: linux-2.6-lttng/include/asm-x86/kdebug.h
===================================================================
--- linux-2.6-lttng.orig/include/asm-x86/kdebug.h	2007-11-02 15:01:53.000000000 -0400
+++ linux-2.6-lttng/include/asm-x86/kdebug.h	2007-11-02 15:02:00.000000000 -0400
@@ -3,6 +3,9 @@
 
 #include <linux/notifier.h>
 
+#include <linux/ptrace.h>
+#include <asm/system.h>
+
 struct pt_regs;
 
 /* Grossly misnamed. */
@@ -30,4 +33,13 @@ extern void dump_pagetable(unsigned long
 extern unsigned long oops_begin(void);
 extern void oops_end(unsigned long);
 
+/* trap3/1 are intr gates for kprobes.  So, restore the status of IF,
+ * if necessary, before executing the original int3/1 (trap) handler.
+ */
+static inline void restore_interrupts(struct pt_regs *regs)
+{
+	if (regs->eflags & IF_MASK)
+		local_irq_enable();
+}
+
 #endif
Index: linux-2.6-lttng/include/asm-x86/kprobes_32.h
===================================================================
--- linux-2.6-lttng.orig/include/asm-x86/kprobes_32.h	2007-11-02 15:01:53.000000000 -0400
+++ linux-2.6-lttng/include/asm-x86/kprobes_32.h	2007-11-02 15:02:00.000000000 -0400
@@ -79,15 +79,6 @@ struct kprobe_ctlblk {
 	struct prev_kprobe prev_kprobe;
 };
 
-/* trap3/1 are intr gates for kprobes.  So, restore the status of IF,
- * if necessary, before executing the original int3/1 (trap) handler.
- */
-static inline void restore_interrupts(struct pt_regs *regs)
-{
-	if (regs->eflags & IF_MASK)
-		local_irq_enable();
-}
-
 extern int kprobe_exceptions_notify(struct notifier_block *self,
 				    unsigned long val, void *data);
 extern int kprobe_fault_handler(struct pt_regs *regs, int trapnr);
Index: linux-2.6-lttng/include/asm-x86/kprobes_64.h
===================================================================
--- linux-2.6-lttng.orig/include/asm-x86/kprobes_64.h	2007-11-02 15:02:10.000000000 -0400
+++ linux-2.6-lttng/include/asm-x86/kprobes_64.h	2007-11-02 15:02:22.000000000 -0400
@@ -72,15 +72,6 @@ struct kprobe_ctlblk {
 	struct prev_kprobe prev_kprobe;
 };
 
-/* trap3/1 are intr gates for kprobes.  So, restore the status of IF,
- * if necessary, before executing the original int3/1 (trap) handler.
- */
-static inline void restore_interrupts(struct pt_regs *regs)
-{
-	if (regs->eflags & IF_MASK)
-		local_irq_enable();
-}
-
 extern int post_kprobe_handler(struct pt_regs *regs);
 extern int kprobe_fault_handler(struct pt_regs *regs, int trapnr);
 extern int kprobe_handler(struct pt_regs *regs);

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

[rfc-patch 4/9] 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

[rfc-patch 5/9] Add __discard section to x86

[Mathieu Desnoyers]

[-- Attachment #1: add-discard-section-to-x86.patch --]
[-- Type: text/plain, Size: 1776 bytes --]

Add a __discard sectionto the linker script. Code produced in this section will
not be put in the vmlinux file. This is useful when we have to calculate the
size of an instruction before actually declaring it (for alignment purposes for
instance). This is used by the immediate values.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Acked-by: H. Peter Anvin <hpa@zytor.com>
CC: Andi Kleen <ak@muc.de>
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>
---
 arch/x86/kernel/vmlinux_32.lds.S |    1 +
 arch/x86/kernel/vmlinux_64.lds.S |    1 +
 2 files changed, 2 insertions(+)

Index: linux-2.6-lttng/arch/x86/kernel/vmlinux_32.lds.S
===================================================================
--- linux-2.6-lttng.orig/arch/x86/kernel/vmlinux_32.lds.S	2007-11-14 14:10:43.000000000 -0500
+++ linux-2.6-lttng/arch/x86/kernel/vmlinux_32.lds.S	2007-11-14 14:11:32.000000000 -0500
@@ -205,6 +205,7 @@ SECTIONS
   /* Sections to be discarded */
   /DISCARD/ : {
 	*(.exitcall.exit)
+	*(__discard)
 	}
 
   STABS_DEBUG
Index: linux-2.6-lttng/arch/x86/kernel/vmlinux_64.lds.S
===================================================================
--- linux-2.6-lttng.orig/arch/x86/kernel/vmlinux_64.lds.S	2007-11-14 14:10:46.000000000 -0500
+++ linux-2.6-lttng/arch/x86/kernel/vmlinux_64.lds.S	2007-11-14 14:11:48.000000000 -0500
@@ -227,6 +227,7 @@ SECTIONS
   /DISCARD/ : {
 	*(.exitcall.exit)
 	*(.eh_frame)
+	*(__discard)
 	}
 
   STABS_DEBUG

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

[rfc-patch 6/9] 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: 13879 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 immediate_mutex).
- Put immediate_set and _immediate_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 __immediate section. Use smallest types required for size (char).

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 
 arch/x86/kernel/Makefile_32 |    1 
 arch/x86/kernel/Makefile_64 |    1 
 arch/x86/kernel/immediate.c |  153 ++++++++++++++++++++++++++++++++++++++++++++
 arch/x86/kernel/traps_32.c  |   10 +-
 include/asm-x86/immediate.h |  110 +++++++++++++++++++++++++++++++
 6 files changed, 272 insertions(+), 4 deletions(-)

Index: linux-2.6-lttng/arch/x86/kernel/Makefile_32
===================================================================
--- linux-2.6-lttng.orig/arch/x86/kernel/Makefile_32	2007-11-16 11:37:44.000000000 -0500
+++ linux-2.6-lttng/arch/x86/kernel/Makefile_32	2007-11-16 11:37:50.000000000 -0500
@@ -35,6 +35,7 @@ obj-$(CONFIG_KPROBES)		+= kprobes_32.o
 obj-$(CONFIG_MODULES)		+= module_32.o
 obj-y				+= sysenter_32.o vsyscall_32.o
 obj-$(CONFIG_ACPI_SRAT) 	+= srat_32.o
+obj-$(CONFIG_IMMEDIATE)		+= immediate.o
 obj-$(CONFIG_EFI) 		+= efi_32.o efi_stub_32.o
 obj-$(CONFIG_DOUBLEFAULT) 	+= doublefault_32.o
 obj-$(CONFIG_VM86)		+= vm86_32.o
Index: linux-2.6-lttng/arch/x86/kernel/traps_32.c
===================================================================
--- linux-2.6-lttng.orig/arch/x86/kernel/traps_32.c	2007-11-16 11:37:44.000000000 -0500
+++ linux-2.6-lttng/arch/x86/kernel/traps_32.c	2007-11-16 12:31:23.000000000 -0500
@@ -544,7 +544,7 @@ fastcall void do_##name(struct pt_regs *
 }
 
 DO_VM86_ERROR_INFO( 0, SIGFPE,  "divide error", divide_error, FPE_INTDIV, regs->eip)
-#ifndef CONFIG_KPROBES
+#if !defined(CONFIG_KPROBES) && !defined(CONFIG_IMMEDIATE)
 DO_VM86_ERROR( 3, SIGTRAP, "int3", int3)
 #endif
 DO_VM86_ERROR( 4, SIGSEGV, "overflow", overflow)
@@ -786,7 +786,7 @@ void restart_nmi(void)
 	acpi_nmi_enable();
 }
 
-#ifdef CONFIG_KPROBES
+#if defined(CONFIG_KPROBES) || defined(CONFIG_IMMEDIATE)
 fastcall void __kprobes do_int3(struct pt_regs *regs, long error_code)
 {
 	trace_hardirqs_fixup();
@@ -794,8 +794,10 @@ fastcall void __kprobes do_int3(struct p
 	if (notify_die(DIE_INT3, "int3", regs, error_code, 3, SIGTRAP)
 			== NOTIFY_STOP)
 		return;
-	/* This is an interrupt gate, because kprobes wants interrupts
-	disabled.  Normal trap handlers don't. */
+	/*
+	 * This is an interrupt gate, because kprobes and immediate values wants
+	 * interrupts disabled.  Normal trap handlers don't.
+	 */
 	restore_interrupts(regs);
 	do_trap(3, SIGTRAP, "int3", 1, regs, error_code, NULL);
 }
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	2007-11-16 12:08:45.000000000 -0500
@@ -0,0 +1,110 @@
+#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>
+
+struct __immediate {
+	unsigned long var;	/* Pointer to the identifier variable of the
+				 * immediate value
+				 */
+	unsigned long immediate;/*
+				 * Pointer to the memory location of the
+				 * immediate value within the instruction.
+				 */
+	unsigned char size;	/* Type size. */
+} __attribute__ ((packed));
+
+/**
+ * immediate_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 _immediate_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).
+ *
+ * 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 modification of the immediate value without knowing the size of
+ * the opcode used by the compiler. The operand size is known in advance.
+ */
+#define immediate_read(name)						\
+	({								\
+		__typeof__(name##__immediate) value;			\
+		switch (sizeof(value)) {				\
+		case 1:							\
+			asm(".section __immediate,\"a\",@progbits\n\t"	\
+				_ASM_PTR "%c1, (3f)-%c2\n\t"		\
+				".byte %c2\n\t"				\
+				".previous\n\t"				\
+				"2:\n\t"				\
+				"mov $0,%0\n\t"				\
+				"3:\n\t"				\
+				: "=q" (value)				\
+				: "i" (&name##__immediate),		\
+				  "i" (sizeof(value)));			\
+			break;						\
+		case 2:							\
+		case 4:							\
+			asm(".section __discard,\"\",@progbits\n\t"	\
+				"1:\n\t"				\
+				"mov $0,%0\n\t"				\
+				"2:\n\t"				\
+				".previous\n\t"				\
+				".section __immediate,\"a\",@progbits\n\t" \
+				_ASM_PTR "%c1, (3f)-%c2\n\t"		\
+				".byte %c2\n\t"				\
+				".previous\n\t"				\
+				".org . + ((-.-(2b-1b)) & (%c2-1)), 0x90\n\t" \
+				"mov $0,%0\n\t"				\
+				"3:\n\t"				\
+				: "=r" (value)				\
+				: "i" (&name##__immediate),		\
+				  "i" (sizeof(value)));			\
+			break;						\
+		case 8:							\
+			if (sizeof(long) < 8) {				\
+				value = name##__immediate;		\
+				break;					\
+			}						\
+			asm(".section __discard,\"\",@progbits\n\t"	\
+				"1:\n\t"				\
+				"mov $0xFEFEFEFE01010101,%0\n\t" 	\
+				"2:\n\t"				\
+				".previous\n\t"				\
+				".section __immediate,\"a\",@progbits\n\t" \
+				_ASM_PTR "%c1, (3f)-%c2\n\t"		\
+				".byte %c2\n\t"				\
+				".previous\n\t"				\
+				".org . + ((-.-(2b-1b)) & (%c2-1)), 0x90\n\t" \
+				"mov $0xFEFEFEFE01010101,%0\n\t" 	\
+				"3:\n\t"				\
+				: "=r" (value)				\
+				: "i" (&name##__immediate),		\
+				  "i" (sizeof(value)));			\
+			break;						\
+		default:value = name##__immediate;			\
+			break;						\
+		};							\
+		value;							\
+	})
+
+extern int arch_immediate_update(const struct __immediate *immediate);
+extern void arch_immediate_update_early(const struct __immediate *immediate);
+
+#endif /* _ASM_X86_IMMEDIATE_H */
Index: linux-2.6-lttng/arch/x86/kernel/immediate.c
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6-lttng/arch/x86/kernel/immediate.c	2007-11-16 12:08:45.000000000 -0500
@@ -0,0 +1,153 @@
+/*
+ * Immediate Value - x86 architecture specific code.
+ *
+ * Rationale
+ *
+ * Required because of :
+ * - Erratum 49 fix for Intel PIII.
+ * - Still present on newer processors : Intel Core 2 Duo Processor for Intel
+ *   Centrino Duo Processor Technology Specification Update, AH33.
+ *   Unsynchronized Cross-Modifying Code Operations Can Cause Unexpected
+ *   Instruction Execution Results.
+ *
+ * Permits immediate value modification by XMC with correct serialization.
+ *
+ * Non reentrant for NMI and trap handler instrumentation.
+ *
+ * Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
+ */
+
+#include <linux/preempt.h>
+#include <linux/smp.h>
+#include <linux/notifier.h>
+#include <linux/module.h>
+#include <linux/immediate.h>
+#include <linux/cpu.h>
+
+static atomic_t wait_sync;
+
+static void ipi_busy_loop(void *arg)
+{
+	long value = (long)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) > 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();
+	local_irq_restore(flags);
+}
+
+/**
+ * arch_immediate_update - update one immediate value
+ * @immediate: pointer of type const struct __immediate to update
+ *
+ * Update one immediate value. Must be called with immediate_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).
+ */
+int arch_immediate_update(const struct __immediate *immediate)
+{
+	unsigned long flags;
+	long online_cpus;
+
+	/*
+	 * If the variable and the instruction have the same value, there is
+	 * nothing to do.
+	 */
+	switch (immediate->size) {
+	case 1:	if (*(uint8_t *)immediate->immediate
+				== *(uint8_t *)immediate->var)
+			return 0;
+		break;
+	case 2:	if (*(uint16_t *)immediate->immediate
+				== *(uint16_t *)immediate->var)
+			return 0;
+		break;
+	case 4:	if (*(uint32_t *)immediate->immediate
+				== *(uint32_t *)immediate->var)
+			return 0;
+		break;
+#ifdef CONFIG_X86_64
+	case 8:	if (*(uint64_t *)immediate->immediate
+				== *(uint64_t *)immediate->var)
+			return 0;
+		break;
+#endif
+	default:return -EINVAL;
+	}
+
+	lock_cpu_hotplug();
+	online_cpus = num_online_cpus();
+	atomic_set(&wait_sync, 2 * online_cpus);
+	smp_call_function(ipi_busy_loop, (void *)online_cpus, 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 *)immediate->immediate, (void *)immediate->var,
+			immediate->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);
+	local_irq_restore(flags);
+	unlock_cpu_hotplug();
+	return 0;
+}
+
+/**
+ * arch_immediate_update_early - update one immediate value at boot time
+ * @immediate: pointer of type const struct __immediate to update
+ *
+ * Update one immediate value at boot time.
+ */
+void arch_immediate_update_early(const struct __immediate *immediate)
+{
+	/*
+	 * If the variable and the instruction have the same value, there is
+	 * nothing to do.
+	 */
+	switch (immediate->size) {
+	case 1:	if (*(uint8_t *)immediate->immediate
+				== *(uint8_t *)immediate->var)
+			return;
+		break;
+	case 2:	if (*(uint16_t *)immediate->immediate
+				== *(uint16_t *)immediate->var)
+			return;
+		break;
+	case 4:	if (*(uint32_t *)immediate->immediate
+				== *(uint32_t *)immediate->var)
+			return;
+		break;
+#ifdef CONFIG_X86_64
+	case 8:	if (*(uint64_t *)immediate->immediate
+				== *(uint64_t *)immediate->var)
+			return;
+		break;
+#endif
+	default:return;
+	}
+	memcpy((void *)immediate->immediate, (void *)immediate->var,
+			immediate->size);
+}
Index: linux-2.6-lttng/arch/x86/kernel/Makefile_64
===================================================================
--- linux-2.6-lttng.orig/arch/x86/kernel/Makefile_64	2007-11-16 11:37:44.000000000 -0500
+++ linux-2.6-lttng/arch/x86/kernel/Makefile_64	2007-11-16 11:37:50.000000000 -0500
@@ -35,6 +35,7 @@ obj-$(CONFIG_X86_PM_TIMER)	+= pmtimer_64
 obj-$(CONFIG_X86_VSMP)		+= vsmp_64.o
 obj-$(CONFIG_K8_NB)		+= k8.o
 obj-$(CONFIG_AUDIT)		+= audit_64.o
+obj-$(CONFIG_IMMEDIATE)		+= immediate.o
 
 obj-$(CONFIG_MODULES)		+= module_64.o
 obj-$(CONFIG_PCI)		+= early-quirks.o
Index: linux-2.6-lttng/arch/x86/Kconfig
===================================================================
--- linux-2.6-lttng.orig/arch/x86/Kconfig	2007-11-16 11:37:44.000000000 -0500
+++ linux-2.6-lttng/arch/x86/Kconfig	2007-11-16 12:31:21.000000000 -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

[rfc-patch 7/9] Immediate Values - Powerpc Optimization

[Mathieu Desnoyers]

[-- Attachment #1: immediate-values-powerpc-optimization.patch --]
[-- Type: text/plain, Size: 7530 bytes --]

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

Changelog:
- Put immediate_set and _immediate_set in the architecture independent header.
- Pack the __immediate section. Use smallest types required for size (char).

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
CC: Christoph Hellwig <hch@infradead.org>
CC: Paul Mackerras <paulus@samba.org>
---
 arch/powerpc/Kconfig            |    1 
 arch/powerpc/kernel/Makefile    |    1 
 arch/powerpc/kernel/immediate.c |  103 ++++++++++++++++++++++++++++++++++++++++
 include/asm-powerpc/immediate.h |   73 ++++++++++++++++++++++++++++
 4 files changed, 178 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	2007-11-16 11:08:17.000000000 -0500
@@ -0,0 +1,73 @@
+#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>
+
+struct __immediate {
+	unsigned long var;	/* Identifier variable of the immediate value */
+	unsigned long immediate;/*
+				 * Pointer to the memory location that holds
+				 * the immediate value within the load immediate
+				 * instruction.
+				 */
+	unsigned char size;	/* Type size. */
+} __attribute__ ((packed));
+
+/**
+ * immediate_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 _immediate_read() instead.
+ * Makes sure the 2 bytes update will be atomic by aligning the immediate
+ * value. Use a normal memory read for the 4 bytes immediate because there is no
+ * way to atomically update it without using a seqlock read side, which would
+ * cost more in term of total i-cache and d-cache space than a simple memory
+ * read.
+ */
+#define immediate_read(name)						\
+	({								\
+		__typeof__(name##__immediate) value;			\
+		switch (sizeof(value)) {				\
+		case 1:							\
+			asm(".section __immediate,\"a\",@progbits\n\t"	\
+					PPC_LONG "%c1, ((0f)+3)\n\t"	\
+					".byte 1\n\t"			\
+					".previous\n\t"			\
+					"0:\n\t"			\
+					"li %0,0\n\t"			\
+				: "=r" (value)				\
+				: "i" (&name##__immediate));		\
+			break;						\
+		case 2:							\
+			asm(".section __immediate,\"a\",@progbits\n\t"	\
+					PPC_LONG "%c1, ((0f)+2)\n\t"	\
+					".byte 2\n\t"			\
+					".previous\n\t"			\
+					".align 2\n\t"			\
+					"0:\n\t"			\
+					"li %0,0\n\t"			\
+				: "=r" (value)				\
+				: "i" (&name##__immediate));		\
+			break;						\
+		default:						\
+			value = name##__immediate;			\
+			break;						\
+		};							\
+		value;							\
+	})
+
+extern int arch_immediate_update(const struct __immediate *immediate);
+extern void arch_immediate_update_early(const struct __immediate *immediate);
+
+#endif /* _ASM_POWERPC_IMMEDIATE_H */
Index: linux-2.6-lttng/arch/powerpc/kernel/Makefile
===================================================================
--- linux-2.6-lttng.orig/arch/powerpc/kernel/Makefile	2007-11-16 10:53:01.000000000 -0500
+++ linux-2.6-lttng/arch/powerpc/kernel/Makefile	2007-11-16 11:05:38.000000000 -0500
@@ -91,3 +91,4 @@ obj-$(CONFIG_PPC64)		+= $(obj64-y)
 
 extra-$(CONFIG_PPC_FPU)		+= fpu.o
 extra-$(CONFIG_PPC64)		+= entry_64.o
+obj-$(CONFIG_IMMEDIATE)		+= immediate.o
Index: linux-2.6-lttng/arch/powerpc/kernel/immediate.c
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6-lttng/arch/powerpc/kernel/immediate.c	2007-11-16 11:05:38.000000000 -0500
@@ -0,0 +1,103 @@
+/*
+ * Powerpc optimized immediate values enabling/disabling.
+ *
+ * Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
+ */
+
+#include <linux/module.h>
+#include <linux/immediate.h>
+#include <linux/string.h>
+#include <linux/kprobes.h>
+#include <asm/cacheflush.h>
+#include <asm/page.h>
+
+#define LI_OPCODE_LEN	2
+
+/**
+ * arch_immediate_update - update one immediate value
+ * @immediate: pointer of type const struct __immediate to update
+ *
+ * Update one immediate value. Must be called with immediate_mutex held.
+ */
+int arch_immediate_update(const struct __immediate *immediate)
+{
+#ifdef CONFIG_KPROBES
+	kprobe_opcode_t *insn;
+	/*
+	 * Fail if a kprobe has been set on this instruction.
+	 * (TODO: we could eventually do better and modify all the (possibly
+	 * nested) kprobes for this site if kprobes had an API for this.
+	 */
+	switch (immediate->size) {
+	case 1:	/* The uint8_t points to the 3rd byte of the
+		 * instruction */
+		insn = (void *)(immediate->immediate - 1 - LI_OPCODE_LEN);
+		break;
+	case 2:	insn = (void *)(immediate->immediate - LI_OPCODE_LEN);
+		break;
+	default:
+	return -EINVAL;
+	}
+
+	if (unlikely(*insn == BREAKPOINT_INSTRUCTION)) {
+		printk(KERN_WARNING "Immediate value in conflict with kprobe. "
+				    "Variable at %p, "
+				    "instruction at %p, size %lu\n",
+				    (void *)immediate->immediate,
+				    (void *)immediate->var, immediate->size);
+		return -EBUSY;
+	}
+#endif
+
+	/*
+	 * If the variable and the instruction have the same value, there is
+	 * nothing to do.
+	 */
+	switch (immediate->size) {
+	case 1:	if (*(uint8_t *)immediate->immediate
+				== *(uint8_t *)immediate->var)
+			return 0;
+		break;
+	case 2:	if (*(uint16_t *)immediate->immediate
+				== *(uint16_t *)immediate->var)
+			return 0;
+		break;
+	default:return -EINVAL;
+	}
+	memcpy((void *)immediate->immediate, (void *)immediate->var,
+			immediate->size);
+	flush_icache_range((unsigned long)immediate->immediate,
+		(unsigned long)immediate->immediate + immediate->size);
+	return 0;
+}
+
+/**
+ * arch_immediate_update_early - update one immediate value at boot time
+ * @immediate: pointer of type const struct __immediate to update
+ *
+ * Update one immediate value at boot time.
+ * We can use flush_icache_range, since the cpu identification has been done in
+ * the early_init stage.
+ */
+void arch_immediate_update_early(const struct __immediate *immediate)
+{
+	/*
+	 * If the variable and the instruction have the same value, there is
+	 * nothing to do.
+	 */
+	switch (immediate->size) {
+	case 1:	if (*(uint8_t *)immediate->immediate
+				== *(uint8_t *)immediate->var)
+			return;
+		break;
+	case 2:	if (*(uint16_t *)immediate->immediate
+				== *(uint16_t *)immediate->var)
+			return;
+		break;
+	default:return;
+	}
+	memcpy((void *)immediate->immediate, (void *)immediate->var,
+			immediate->size);
+	flush_icache_range((unsigned long)immediate->immediate,
+		(unsigned long)immediate->immediate + immediate->size);
+}
Index: linux-2.6-lttng/arch/powerpc/Kconfig
===================================================================
--- linux-2.6-lttng.orig/arch/powerpc/Kconfig	2007-11-16 10:53:01.000000000 -0500
+++ linux-2.6-lttng/arch/powerpc/Kconfig	2007-11-16 11:05:38.000000000 -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

[rfc-patch 8/9] 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: 8837 bytes --]

Changelog:
- Remove immediate_set_early (removed from API).

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
---
 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(immediate_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_IMMEDIATE(char, this_immediate);
+EXPORT_IMMEDIATE_SYMBOL(this_immediate);
+
+
+And use, in the body of a function:
+
+Use immediate_set(this_immediate) to set the immediate value.
+
+Use immediate_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 _immediate_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_IMMEDIATE(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

[rfc-patch 9/9] Scheduler Profiling - Use Immediate Values

[Mathieu Desnoyers]

[-- Attachment #1: profiling-use-immediate-values.patch --]
[-- Type: text/plain, Size: 5769 bytes --]

Use immediate values with lower d-cache hit in optimized version as a
condition for scheduler profiling call.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
---
 drivers/kvm/kvm_main.c  |    3 ++-
 include/linux/profile.h |    5 +++--
 kernel/profile.c        |   22 +++++++++++-----------
 kernel/sched_fair.c     |    6 +-----
 4 files changed, 17 insertions(+), 19 deletions(-)

Index: linux-2.6-lttng/kernel/profile.c
===================================================================
--- linux-2.6-lttng.orig/kernel/profile.c	2007-11-13 09:48:36.000000000 -0500
+++ linux-2.6-lttng/kernel/profile.c	2007-11-13 09:48:37.000000000 -0500
@@ -42,8 +42,8 @@ static int (*timer_hook)(struct pt_regs 
 static atomic_t *prof_buffer;
 static unsigned long prof_len, prof_shift;
 
-int prof_on __read_mostly;
-EXPORT_SYMBOL_GPL(prof_on);
+DEFINE_IMMEDIATE(char, prof_on) __read_mostly;
+EXPORT_IMMEDIATE_SYMBOL_GPL(prof_on);
 
 static cpumask_t prof_cpu_mask = CPU_MASK_ALL;
 #ifdef CONFIG_SMP
@@ -61,7 +61,7 @@ static int __init profile_setup(char * s
 
 	if (!strncmp(str, sleepstr, strlen(sleepstr))) {
 #ifdef CONFIG_SCHEDSTATS
-		prof_on = SLEEP_PROFILING;
+		immediate_set(prof_on, SLEEP_PROFILING);
 		if (str[strlen(sleepstr)] == ',')
 			str += strlen(sleepstr) + 1;
 		if (get_option(&str, &par))
@@ -74,7 +74,7 @@ static int __init profile_setup(char * s
 			"kernel sleep profiling requires CONFIG_SCHEDSTATS\n");
 #endif /* CONFIG_SCHEDSTATS */
 	} else if (!strncmp(str, schedstr, strlen(schedstr))) {
-		prof_on = SCHED_PROFILING;
+		immediate_set(prof_on, SCHED_PROFILING);
 		if (str[strlen(schedstr)] == ',')
 			str += strlen(schedstr) + 1;
 		if (get_option(&str, &par))
@@ -83,7 +83,7 @@ static int __init profile_setup(char * s
 			"kernel schedule profiling enabled (shift: %ld)\n",
 			prof_shift);
 	} else if (!strncmp(str, kvmstr, strlen(kvmstr))) {
-		prof_on = KVM_PROFILING;
+		immediate_set(prof_on, KVM_PROFILING);
 		if (str[strlen(kvmstr)] == ',')
 			str += strlen(kvmstr) + 1;
 		if (get_option(&str, &par))
@@ -93,7 +93,7 @@ static int __init profile_setup(char * s
 			prof_shift);
 	} else if (get_option(&str, &par)) {
 		prof_shift = par;
-		prof_on = CPU_PROFILING;
+		immediate_set(prof_on, CPU_PROFILING);
 		printk(KERN_INFO "kernel profiling enabled (shift: %ld)\n",
 			prof_shift);
 	}
@@ -104,7 +104,7 @@ __setup("profile=", profile_setup);
 
 void __init profile_init(void)
 {
-	if (!prof_on) 
+	if (!_immediate_read(prof_on))
 		return;
  
 	/* only text is profiled */
@@ -293,7 +293,7 @@ void profile_hits(int type, void *__pc, 
 	int i, j, cpu;
 	struct profile_hit *hits;
 
-	if (prof_on != type || !prof_buffer)
+	if (!prof_buffer)
 		return;
 	pc = min((pc - (unsigned long)_stext) >> prof_shift, prof_len - 1);
 	i = primary = (pc & (NR_PROFILE_GRP - 1)) << PROFILE_GRPSHIFT;
@@ -403,7 +403,7 @@ void profile_hits(int type, void *__pc, 
 {
 	unsigned long pc;
 
-	if (prof_on != type || !prof_buffer)
+	if (!prof_buffer)
 		return;
 	pc = ((unsigned long)__pc - (unsigned long)_stext) >> prof_shift;
 	atomic_add(nr_hits, &prof_buffer[min(pc, prof_len - 1)]);
@@ -560,7 +560,7 @@ static int __init create_hash_tables(voi
 	}
 	return 0;
 out_cleanup:
-	prof_on = 0;
+	immediate_set(prof_on, 0);
 	smp_mb();
 	on_each_cpu(profile_nop, NULL, 0, 1);
 	for_each_online_cpu(cpu) {
@@ -587,7 +587,7 @@ static int __init create_proc_profile(vo
 {
 	struct proc_dir_entry *entry;
 
-	if (!prof_on)
+	if (!_immediate_read(prof_on))
 		return 0;
 	if (create_hash_tables())
 		return -1;
Index: linux-2.6-lttng/include/linux/profile.h
===================================================================
--- linux-2.6-lttng.orig/include/linux/profile.h	2007-11-13 09:48:36.000000000 -0500
+++ linux-2.6-lttng/include/linux/profile.h	2007-11-13 09:48:37.000000000 -0500
@@ -7,10 +7,11 @@
 #include <linux/init.h>
 #include <linux/cpumask.h>
 #include <linux/cache.h>
+#include <linux/immediate.h>
 
 #include <asm/errno.h>
 
-extern int prof_on __read_mostly;
+DECLARE_IMMEDIATE(char, prof_on) __read_mostly;
 
 #define CPU_PROFILING	1
 #define SCHED_PROFILING	2
@@ -38,7 +39,7 @@ static inline void profile_hit(int type,
 	/*
 	 * Speedup for the common (no profiling enabled) case:
 	 */
-	if (unlikely(prof_on == type))
+	if (unlikely(immediate_read(prof_on) == type))
 		profile_hits(type, ip, 1);
 }
 
Index: linux-2.6-lttng/drivers/kvm/kvm_main.c
===================================================================
--- linux-2.6-lttng.orig/drivers/kvm/kvm_main.c	2007-11-13 09:48:36.000000000 -0500
+++ linux-2.6-lttng/drivers/kvm/kvm_main.c	2007-11-13 09:48:37.000000000 -0500
@@ -2054,7 +2054,8 @@ again:
 	/*
 	 * Profile KVM exit RIPs:
 	 */
-	if (unlikely(prof_on == KVM_PROFILING)) {
+
+	if (unlikely(immediate_read(prof_on) == KVM_PROFILING)) {
 		kvm_x86_ops->cache_regs(vcpu);
 		profile_hit(KVM_PROFILING, (void *)vcpu->rip);
 	}
Index: linux-2.6-lttng/kernel/sched_fair.c
===================================================================
--- linux-2.6-lttng.orig/kernel/sched_fair.c	2007-11-13 09:48:36.000000000 -0500
+++ linux-2.6-lttng/kernel/sched_fair.c	2007-11-13 09:48:37.000000000 -0500
@@ -455,12 +455,8 @@ static void enqueue_sleeper(struct cfs_r
 		 * get a milliseconds-range estimation of the amount of
 		 * time that the task spent sleeping:
 		 */
-		if (unlikely(prof_on == SLEEP_PROFILING)) {
-			struct task_struct *tsk = task_of(se);
-
-			profile_hits(SLEEP_PROFILING, (void *)get_wchan(tsk),
+		profile_hits(SLEEP_PROFILING, (void *)get_wchan(task_of(se)),
 				     delta >> 20);
-		}
 	}
 #endif
 }

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

Re: [rfc-patch 0/9] Immediate Values for 2.6.24-rc2-git5

[Borislav Petkov]

On Fri, Nov 16, 2007 at 03:02:38PM -0500, Mathieu Desnoyers wrote:
Hi, 
just a conventions proposal: have you thought of shortening all those
"immediate_foo" prefixes to 'imm_foo', for example? This'll make the 
code much more readable, i think.

- 
Regards/Gruß,
    Boris.

Re: [rfc-patch 0/9] Immediate Values for 2.6.24-rc2-git5

[Mathieu Desnoyers]

* Borislav Petkov (bbpetkov@yahoo.de) wrote:
> On Fri, Nov 16, 2007 at 03:02:38PM -0500, Mathieu Desnoyers wrote:
> Hi, 
> just a conventions proposal: have you thought of shortening all those
> "immediate_foo" prefixes to 'imm_foo', for example? This'll make the 
> code much more readable, i think.
> 

Well, if there are enough supporters of this idea, I'd be happy to
change "immediate_" for "imm_", since it's indeed shorter, easier to
type, and looks better in the code.

Anyone else agrees/disagrees ?

Mathieu

> - 
> Regards/Gruß,
>     Boris.

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

Re: [rfc-patch 0/9] Immediate Values for 2.6.24-rc2-git5

[Mathieu Desnoyers]

* Borislav Petkov (bbpetkov@yahoo.de) wrote:
> On Fri, Nov 16, 2007 at 03:02:38PM -0500, Mathieu Desnoyers wrote:
> Hi, 
> just a conventions proposal: have you thought of shortening all those
> "immediate_foo" prefixes to 'imm_foo', for example? This'll make the 
> code much more readable, i think.
> 

Hrm, a quick grep in the kernel tree shows me that the imm_* namespace
is already quite clobbered (although I do not detect any imm_read or
imm_set). Although I like the imm_ idea, I would like to make sure we do
not break any existing imm_read or imm_set users.

But since I don't see any, I think it would make sense.

> - 
> Regards/Gruß,
>     Boris.

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

Re: [rfc-patch 0/9] Immediate Values for 2.6.24-rc2-git5

[Borislav Petkov]

On Mon, Nov 19, 2007 at 10:31:39AM -0500, Mathieu Desnoyers wrote:
> * Borislav Petkov (bbpetkov@yahoo.de) wrote:
> > On Fri, Nov 16, 2007 at 03:02:38PM -0500, Mathieu Desnoyers wrote:
> > Hi, 
> > just a conventions proposal: have you thought of shortening all those
> > "immediate_foo" prefixes to 'imm_foo', for example? This'll make the 
> > code much more readable, i think.
> > 
> 
> Hrm, a quick grep in the kernel tree shows me that the imm_* namespace
> is already quite clobbered (although I do not detect any imm_read or
> imm_set). 

Right, something called "low level driver for the IOMEGA MatchMaker"
(drivers/scsi/imm.c) has gotten hold of the imm_* prefix already so there might
be a problem later, probably. Nevertheless, you could use the imm_ prefix or
choose some other 3-n letter prefix:

immed_* (3 matches)
imme_* (no matches but dumb)
imd_* (none!)
immv_* (none, v like [v]alues), etc.
...

-- 
Regards/Gruß,
    Boris.

Re: [rfc-patch 0/9] Immediate Values for 2.6.24-rc2-git5

[Mathieu Desnoyers]

* Borislav Petkov (bbpetkov@yahoo.de) wrote:
> On Mon, Nov 19, 2007 at 10:31:39AM -0500, Mathieu Desnoyers wrote:
> > * Borislav Petkov (bbpetkov@yahoo.de) wrote:
> > > On Fri, Nov 16, 2007 at 03:02:38PM -0500, Mathieu Desnoyers wrote:
> > > Hi, 
> > > just a conventions proposal: have you thought of shortening all those
> > > "immediate_foo" prefixes to 'imm_foo', for example? This'll make the 
> > > code much more readable, i think.
> > > 
> > 
> > Hrm, a quick grep in the kernel tree shows me that the imm_* namespace
> > is already quite clobbered (although I do not detect any imm_read or
> > imm_set). 
> 
> Right, something called "low level driver for the IOMEGA MatchMaker"
> (drivers/scsi/imm.c) has gotten hold of the imm_* prefix already so there might
> be a problem later, probably. Nevertheless, you could use the imm_ prefix or
> choose some other 3-n letter prefix:
> 
> immed_* (3 matches)
> imme_* (no matches but dumb)
> imd_* (none!)
> immv_* (none, v like [v]alues), etc.
> ...
> 

I'd go for imv_* then, which indeed stands for "IMmediate Values"

> -- 
> Regards/Gruß,
>     Boris.

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