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add sched_getcpu vDSO support 

This brings the call to an actually usable speed.
Quick unscientific benchmark: 14ns : 102ns :: vDSO : syscall
This commit is contained in:
Nathan Zadoks 2016-03-02 17:26:27 +01:00 committed by Rich Felker
parent 98d335735d
commit db66ef1f7d
2 changed files with 33 additions and 0 deletions
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2
arch/x86_64/syscall_arch.h
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@ -64,3 +64,5 @@ static __inline long __syscall6(long n, long a1, long a2, long a3, long a4, long
#define VDSO_USEFUL
#define VDSO_CGT_SYM "__vdso_clock_gettime"
#define VDSO_CGT_VER "LINUX_2.6"
#define VDSO_GETCPU_SYM "__vdso_getcpu"
#define VDSO_GETCPU_VER "LINUX_2.6"

31
src/sched/sched_getcpu.c
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@ -1,12 +1,43 @@
#define _GNU_SOURCE
#include <errno.h>
#include <sched.h>
#include "syscall.h"
#include "atomic.h"
#ifdef VDSO_GETCPU_SYM
void *__vdsosym(const char *, const char *);
static void *volatile vdso_func;
typedef long (*getcpu_f)(unsigned *, unsigned *, void *);
static long getcpu_init(unsigned *cpu, unsigned *node, void *unused)
{
void *p = __vdsosym(VDSO_GETCPU_VER, VDSO_GETCPU_SYM);
getcpu_f f = (getcpu_f)p;
a_cas_p(&vdso_func, (void *)getcpu_init, p);
return f ? f(cpu, node, unused) : -ENOSYS;
}
static void *volatile vdso_func = (void *)getcpu_init;
#endif
int sched_getcpu(void)
{
int r;
unsigned cpu;
#ifdef VDSO_GETCPU_SYM
getcpu_f f = (getcpu_f)vdso_func;
if (f) {
r = f(&cpu, 0, 0);
if (!r) return cpu;
if (r != -ENOSYS) return __syscall_ret(r);
}
#endif
r = __syscall(SYS_getcpu, &cpu, 0, 0);
if (!r) return cpu;
return __syscall_ret(r);