diff options
Diffstat (limited to 'arch/x86/vdso/vgetcpu.c')
-rw-r--r-- | arch/x86/vdso/vgetcpu.c | 50 |
1 files changed, 50 insertions, 0 deletions
diff --git a/arch/x86/vdso/vgetcpu.c b/arch/x86/vdso/vgetcpu.c new file mode 100644 index 0000000..91f6e85 --- /dev/null +++ b/arch/x86/vdso/vgetcpu.c @@ -0,0 +1,50 @@ +/* + * 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 *tcache) +{ + 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) { + /* 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) + *node = p >> 12; + return 0; +} + +long getcpu(unsigned *cpu, unsigned *node, struct getcpu_cache *tcache) + __attribute__((weak, alias("__vdso_getcpu"))); |