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Message-Id: <1456839940-10330-1-git-send-email-nathan@nathan7.eu>
Date: Tue, 1 Mar 2016 14:45:40 +0100
From: Nathan Zadoks <nathan@...han7.eu>
To: musl@...ts.openwall.com
Cc: Nathan Zadoks <nathan@...han7.eu>
Subject: [PATCH] add sched_getcpu, with vDSO support
This is a GNU extension, but a fairly minor one, for a system call that
otherwise has no libc wrapper.
Adding it was discussed previously, without any objections:
http://www.openwall.com/lists/musl/2015/05/08/24
---
I've done some cleanup and added vDSO support, since it seems to make a
significant perf difference. (about 14ns/vDSO call, vs about 102ns/syscall)
I've only added vDSO support for x86_64, since it doesn't exist on i386, and I
don't see any vDSO handling at all on x32.
The vDSO function is also available on PowerPC, but I don't have any machines
for testing that on, so I've left that out too.
---
arch/x86_64/syscall_arch.h | 2 ++
include/sched.h | 1 +
src/sched/sched_getcpu.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 48 insertions(+)
create mode 100644 src/sched/sched_getcpu.c
diff --git a/arch/x86_64/syscall_arch.h b/arch/x86_64/syscall_arch.h
index a7a7b5a..54e05ff 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/include/sched.h b/include/sched.h
index 3e34a72..7e88f09 100644
--- a/include/sched.h
+++ b/include/sched.h
@@ -76,6 +76,7 @@ void free(void *);
typedef struct cpu_set_t { unsigned long __bits[128/sizeof(long)]; } cpu_set_t;
int __sched_cpucount(size_t, const cpu_set_t *);
+int sched_getcpu(void);
int sched_getaffinity(pid_t, size_t, cpu_set_t *);
int sched_setaffinity(pid_t, size_t, const cpu_set_t *);
diff --git a/src/sched/sched_getcpu.c b/src/sched/sched_getcpu.c
new file mode 100644
index 0000000..ed5e331
--- /dev/null
+++ b/src/sched/sched_getcpu.c
@@ -0,0 +1,45 @@
+#define _GNU_SOURCE
+#include <stdlib.h>
+#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 *);
+
+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_CGT_SYM
+ getcpu_f f = (getcpu_f)vdso_func;
+ if (f) {
+ r = f(&cpu, NULL, NULL);
+ if (!r) return cpu;
+ if (r != -ENOSYS) return __syscall_ret(r);
+ }
+#endif
+
+ r = __syscall(SYS_getcpu, &cpu, NULL, NULL);
+ if (!r) return cpu;
+ return __syscall_ret(r);
+}
--
2.7.1
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