kernel-ark/arch/x86/vdso/vgetcpu.c
Ingo Molnar 4307d1e5ad 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>
2007-11-17 16:27:00 +01:00

36 lines
827 B
C

/*
* Copyright 2006 Andi Kleen, SUSE Labs.
* Subject to the GNU Public License, v.2
*
* Fast user context implementation of getcpu()
*/
#include <linux/kernel.h>
#include <linux/getcpu.h>
#include <linux/jiffies.h>
#include <linux/time.h>
#include <asm/vsyscall.h>
#include <asm/vgtod.h>
#include "vextern.h"
long __vdso_getcpu(unsigned *cpu, unsigned *node, struct getcpu_cache *unused)
{
unsigned int dummy, p;
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 (cpu)
*cpu = p & 0xfff;
if (node)
*node = p >> 12;
return 0;
}
long getcpu(unsigned *cpu, unsigned *node, struct getcpu_cache *tcache)
__attribute__((weak, alias("__vdso_getcpu")));