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authorIngo Molnar <mingo@elte.hu>2007-11-07 18:37:48 +0100
committerThomas Gleixner <tglx@apollo.(none)>2007-11-17 16:27:00 +0100
commit4307d1e5ada595c87f9a4d16db16ba5edb70dcb1 (patch)
treebae1a90cc162a0d5bd1a78290ffb1f445fc07d80 /arch/x86
parent434b3d3209a8d8dcda63c3b14815659f4671b0a8 (diff)
x86: ignore the sys_getcpu() tcache parameter
dont use the vgetcpu tcache - it's causing problems with tasks migrating, they'll see the old cache up to a jiffy after the migration, further increasing the costs of the migration. In the worst case they see a complete bogus information from the tcache, when a sys_getcpu() call "invalidated" the cache info by incrementing the jiffies _and_ the cpuid info in the cache and the following vdso_getcpu() call happens after vdso_jiffies have been incremented. Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Ulrich Drepper <drepper@redhat.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'arch/x86')
-rw-r--r--arch/x86/vdso/vgetcpu.c19
1 files changed, 2 insertions, 17 deletions
diff --git a/arch/x86/vdso/vgetcpu.c b/arch/x86/vdso/vgetcpu.c
index 91f6e85d0fc..3b1ae1abfba 100644
--- a/arch/x86/vdso/vgetcpu.c
+++ b/arch/x86/vdso/vgetcpu.c
@@ -13,32 +13,17 @@
#include <asm/vgtod.h>
#include "vextern.h"
-long __vdso_getcpu(unsigned *cpu, unsigned *node, struct getcpu_cache *tcache)
+long __vdso_getcpu(unsigned *cpu, unsigned *node, struct getcpu_cache *unused)
{
unsigned int dummy, p;
- unsigned long j = 0;
- /* Fast cache - only recompute value once per jiffies and avoid
- relatively costly rdtscp/cpuid otherwise.
- This works because the scheduler usually keeps the process
- on the same CPU and this syscall doesn't guarantee its
- results anyways.
- We do this here because otherwise user space would do it on
- its own in a likely inferior way (no access to jiffies).
- If you don't like it pass NULL. */
- if (tcache && tcache->blob[0] == (j = *vdso_jiffies)) {
- p = tcache->blob[1];
- } else if (*vdso_vgetcpu_mode == VGETCPU_RDTSCP) {
+ if (*vdso_vgetcpu_mode == VGETCPU_RDTSCP) {
/* Load per CPU data from RDTSCP */
rdtscp(dummy, dummy, p);
} else {
/* Load per CPU data from GDT */
asm("lsl %1,%0" : "=r" (p) : "r" (__PER_CPU_SEG));
}
- if (tcache) {
- tcache->blob[0] = j;
- tcache->blob[1] = p;
- }
if (cpu)
*cpu = p & 0xfff;
if (node)