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authorNathan Zadoks <nathan@nathan7.eu>2016-03-02 17:26:27 +0100
committerRich Felker <dalias@aerifal.cx>2016-03-02 21:35:40 -0500
commitdb66ef1f7db7c5b672591a97a97bc789c9efe2f3 (patch)
tree6934edee491e19a09bbcbfff2bf7426d18e7a2d6 /src/sched
parent98d335735d64ee34a34cb9c08ea2cb51a076d2a1 (diff)
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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
Diffstat (limited to 'src/sched')
-rw-r--r--src/sched/sched_getcpu.c31
1 files changed, 31 insertions, 0 deletions
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 <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);