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Date: Wed, 21 Apr 2010 16:08:14 +0100
From: "Jan Beulich" <JBeulich@...ell.com>
To: <mingo@...e.hu>, <tglx@...utronix.de>, <hpa@...or.com>
Cc: <linux-kernel@...r.kernel.org>
Subject: [PATCH] x86-64: reduce SMP locks table size
... by using relative pointers instead of absolute ones, thus cutting
the table size by half.
Signed-off-by: Jan Beulich <jbeulich@...ell.com>
---
arch/x86/include/asm/alternative-asm.h | 4 +-
arch/x86/include/asm/alternative.h | 4 +-
arch/x86/kernel/alternative.c | 45 ++++++++++++++++++---------------
3 files changed, 29 insertions(+), 24 deletions(-)
--- linux-2.6.34-rc5/arch/x86/include/asm/alternative-asm.h 2010-02-24 19:52:17.000000000 +0100
+++ 2.6.34-rc5-x86_64-smp-locks-reduce-size/arch/x86/include/asm/alternative-asm.h 2010-04-15 11:58:18.000000000 +0200
@@ -6,8 +6,8 @@
.macro LOCK_PREFIX
1: lock
.section .smp_locks,"a"
- _ASM_ALIGN
- _ASM_PTR 1b
+ .balign 4
+ .long 1b - .
.previous
.endm
#else
--- linux-2.6.34-rc5/arch/x86/include/asm/alternative.h 2010-04-20 16:07:30.000000000 +0200
+++ 2.6.34-rc5-x86_64-smp-locks-reduce-size/arch/x86/include/asm/alternative.h 2010-04-15 11:58:18.000000000 +0200
@@ -30,8 +30,8 @@
#ifdef CONFIG_SMP
#define LOCK_PREFIX \
".section .smp_locks,\"a\"\n" \
- _ASM_ALIGN "\n" \
- _ASM_PTR "661f\n" /* address */ \
+ ".balign 4\n" \
+ ".long 661f - .\n" /* offset */ \
".previous\n" \
"661:\n\tlock; "
--- linux-2.6.34-rc5/arch/x86/kernel/alternative.c 2010-04-20 16:07:31.000000000 +0200
+++ 2.6.34-rc5-x86_64-smp-locks-reduce-size/arch/x86/kernel/alternative.c 2010-04-15 11:58:18.000000000 +0200
@@ -194,7 +194,7 @@ static void __init_or_module add_nops(vo
}
extern struct alt_instr __alt_instructions[], __alt_instructions_end[];
-extern u8 *__smp_locks[], *__smp_locks_end[];
+extern s32 __smp_locks[], __smp_locks_end[];
static void *text_poke_early(void *addr, const void *opcode, size_t len);
/* Replace instructions with better alternatives for this CPU type.
@@ -235,37 +235,39 @@ void __init_or_module apply_alternatives
#ifdef CONFIG_SMP
-static void alternatives_smp_lock(u8 **start, u8 **end, u8 *text, u8 *text_end)
+static void alternatives_smp_lock(const s32 *start, const s32 *end,
+ u8 *text, u8 *text_end)
{
- u8 **ptr;
+ const s32 *poff;
mutex_lock(&text_mutex);
- for (ptr = start; ptr < end; ptr++) {
- if (*ptr < text)
- continue;
- if (*ptr > text_end)
+ for (poff = start; poff < end; poff++) {
+ u8 *ptr = (u8 *)poff + *poff;
+
+ if (!*poff || ptr < text || ptr >= text_end)
continue;
/* turn DS segment override prefix into lock prefix */
- text_poke(*ptr, ((unsigned char []){0xf0}), 1);
+ text_poke(ptr, ((unsigned char []){0xf0}), 1);
};
mutex_unlock(&text_mutex);
}
-static void alternatives_smp_unlock(u8 **start, u8 **end, u8 *text, u8 *text_end)
+static void alternatives_smp_unlock(const s32 *start, const s32 *end,
+ u8 *text, u8 *text_end)
{
- u8 **ptr;
+ const s32 *poff;
if (noreplace_smp)
return;
mutex_lock(&text_mutex);
- for (ptr = start; ptr < end; ptr++) {
- if (*ptr < text)
- continue;
- if (*ptr > text_end)
+ for (poff = start; poff < end; poff++) {
+ u8 *ptr = (u8 *)poff + *poff;
+
+ if (!*poff || ptr < text || ptr >= text_end)
continue;
/* turn lock prefix into DS segment override prefix */
- text_poke(*ptr, ((unsigned char []){0x3E}), 1);
+ text_poke(ptr, ((unsigned char []){0x3E}), 1);
};
mutex_unlock(&text_mutex);
}
@@ -276,8 +278,8 @@ struct smp_alt_module {
char *name;
/* ptrs to lock prefixes */
- u8 **locks;
- u8 **locks_end;
+ const s32 *locks;
+ const s32 *locks_end;
/* .text segment, needed to avoid patching init code ;) */
u8 *text;
@@ -398,16 +400,19 @@ void alternatives_smp_switch(int smp)
int alternatives_text_reserved(void *start, void *end)
{
struct smp_alt_module *mod;
- u8 **ptr;
+ const s32 *poff;
u8 *text_start = start;
u8 *text_end = end;
list_for_each_entry(mod, &smp_alt_modules, next) {
if (mod->text > text_end || mod->text_end < text_start)
continue;
- for (ptr = mod->locks; ptr < mod->locks_end; ptr++)
- if (text_start <= *ptr && text_end >= *ptr)
+ for (poff = mod->locks; poff < mod->locks_end; poff++) {
+ const u8 *ptr = (const u8 *)poff + *poff;
+
+ if (text_start <= ptr && text_end > ptr)
return 1;
+ }
}
return 0;
--
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