arch/x86/vdso/vgetcpu.c

   1 /*
   2  * Copyright 2006 Andi Kleen, SUSE Labs.
   3  * Subject to the GNU Public License, v.2
   4  *
   5  * Fast user context implementation of getcpu()
   6  */
   7
   8 #include <linux/kernel.h>
   9 #include <linux/getcpu.h>
  10 #include <linux/jiffies.h>
  11 #include <linux/time.h>
  12 #include <asm/vsyscall.h>
  13 #include <asm/vgtod.h>
  14
  15 notrace long
  16 __vdso_getcpu(unsigned *cpu, unsigned *node, struct getcpu_cache *unused)
  17 {
  18         unsigned int p;
  19
  20         if (VVAR(vgetcpu_mode) == VGETCPU_RDTSCP) {
  21                 /* Load per CPU data from RDTSCP */
  22                 native_read_tscp(&p);
  23         } else {
  24                 /* Load per CPU data from GDT */
  25                 asm("lsl %1,%0" : "=r" (p) : "r" (__PER_CPU_SEG));
  26         }
  27         if (cpu)
  28                 *cpu = p & 0xfff;
  29         if (node)
  30                 *node = p >> 12;
  31         return 0;
  32 }
  33
  34 long getcpu(unsigned *cpu, unsigned *node, struct getcpu_cache *tcache)
  35         __attribute__((weak, alias("__vdso_getcpu")));