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| author | Ingo Molnar <mingo@elte.hu> | 2007-11-07 18:37:48 +0100 |
|---|---|---|
| committer | Thomas Gleixner <tglx@apollo.(none)> | 2007-11-17 16:27:00 +0100 |
| commit | 4307d1e5ada595c87f9a4d16db16ba5edb70dcb1 (patch) | |
| tree | bae1a90cc162a0d5bd1a78290ffb1f445fc07d80 /arch | |
| parent | 434b3d3209a8d8dcda63c3b14815659f4671b0a8 (diff) | |
| download | linux-4307d1e5ada595c87f9a4d16db16ba5edb70dcb1.tar.gz linux-4307d1e5ada595c87f9a4d16db16ba5edb70dcb1.tar.bz2 linux-4307d1e5ada595c87f9a4d16db16ba5edb70dcb1.zip | |
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')
| -rw-r--r-- | arch/x86/vdso/vgetcpu.c | 19 |
1 files changed, 2 insertions, 17 deletions
diff --git a/arch/x86/vdso/vgetcpu.c b/arch/x86/vdso/vgetcpu.c index 91f6e85d0fc2..3b1ae1abfba9 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) |