51 lines
1.4 KiB
C
51 lines
1.4 KiB
C
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/*
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* Copyright 2006 Andi Kleen, SUSE Labs.
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* Subject to the GNU Public License, v.2
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*
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* Fast user context implementation of getcpu()
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*/
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#include <linux/kernel.h>
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#include <linux/getcpu.h>
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#include <linux/jiffies.h>
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#include <linux/time.h>
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#include <asm/vsyscall.h>
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#include <asm/vgtod.h>
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#include "vextern.h"
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long __vdso_getcpu(unsigned *cpu, unsigned *node, struct getcpu_cache *tcache)
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{
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unsigned int dummy, p;
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unsigned long j = 0;
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/* Fast cache - only recompute value once per jiffies and avoid
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relatively costly rdtscp/cpuid otherwise.
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This works because the scheduler usually keeps the process
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on the same CPU and this syscall doesn't guarantee its
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results anyways.
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We do this here because otherwise user space would do it on
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its own in a likely inferior way (no access to jiffies).
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If you don't like it pass NULL. */
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if (tcache && tcache->blob[0] == (j = *vdso_jiffies)) {
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p = tcache->blob[1];
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} else if (*vdso_vgetcpu_mode == VGETCPU_RDTSCP) {
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/* Load per CPU data from RDTSCP */
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rdtscp(dummy, dummy, p);
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} else {
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/* Load per CPU data from GDT */
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asm("lsl %1,%0" : "=r" (p) : "r" (__PER_CPU_SEG));
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}
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if (tcache) {
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tcache->blob[0] = j;
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tcache->blob[1] = p;
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}
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if (cpu)
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*cpu = p & 0xfff;
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if (node)
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*node = p >> 12;
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return 0;
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}
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long getcpu(unsigned *cpu, unsigned *node, struct getcpu_cache *tcache)
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__attribute__((weak, alias("__vdso_getcpu")));
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