From 4307d1e5ada595c87f9a4d16db16ba5edb70dcb1 Mon Sep 17 00:00:00 2001 From: Ingo Molnar Date: Wed, 7 Nov 2007 18:37:48 +0100 Subject: 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 Signed-off-by: Ulrich Drepper Signed-off-by: Thomas Gleixner --- arch/x86/vdso/vgetcpu.c | 19 ++----------------- 1 file changed, 2 insertions(+), 17 deletions(-) (limited to 'arch/x86/vdso') 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 #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) -- cgit v1.2.3