From db66ef1f7db7c5b672591a97a97bc789c9efe2f3 Mon Sep 17 00:00:00 2001 From: Nathan Zadoks Date: Wed, 2 Mar 2016 17:26:27 +0100 Subject: [PATCH] add sched_getcpu vDSO support This brings the call to an actually usable speed. Quick unscientific benchmark: 14ns : 102ns :: vDSO : syscall --- arch/x86_64/syscall_arch.h | 2 ++ src/sched/sched_getcpu.c | 31 +++++++++++++++++++++++++++++++ 2 files changed, 33 insertions(+) diff --git a/arch/x86_64/syscall_arch.h b/arch/x86_64/syscall_arch.h index a7a7b5a6..54e05ff6 100644 --- a/arch/x86_64/syscall_arch.h +++ b/arch/x86_64/syscall_arch.h @@ -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" diff --git a/src/sched/sched_getcpu.c b/src/sched/sched_getcpu.c index 760e4d5b..e08cfdf1 100644 --- a/src/sched/sched_getcpu.c +++ b/src/sched/sched_getcpu.c @@ -1,12 +1,43 @@ #define _GNU_SOURCE +#include #include #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); -- 2.25.1