When available, use the cpu_id field from __rseq_abi on Linux to implement sched_getcpu(). Fall-back on the vgetcpu vDSO if unavailable.
Benchmarks: x86-64: Intel E5-2630 [email protected], 16-core, hyperthreading glibc sched_getcpu(): 13.7 ns (baseline) glibc sched_getcpu() using rseq: 2.5 ns (speedup: 5.5x) inline load cpuid from __rseq_abi TLS: 0.8 ns (speedup: 17.1x) CC: Carlos O'Donell <[email protected]> CC: Florian Weimer <[email protected]> CC: Joseph Myers <[email protected]> CC: Szabolcs Nagy <[email protected]> CC: Thomas Gleixner <[email protected]> CC: Ben Maurer <[email protected]> CC: Peter Zijlstra <[email protected]> CC: "Paul E. McKenney" <[email protected]> CC: Boqun Feng <[email protected]> CC: Will Deacon <[email protected]> CC: Paul Turner <[email protected]> CC: [email protected] CC: [email protected] CC: [email protected] --- Changes since v1: - rseq is only used if both __NR_rseq and RSEQ_SIG are defined. Changes since v2: - remove duplicated __rseq_abi extern declaration. Changes since v3: - update ChangeLog. Changes since v4: - Use atomic_load_relaxed to load the __rseq_abi.cpu_id field, a consequence of the fact that __rseq_abi is not volatile anymore. - Include atomic.h which provides atomic_load_relaxed. Changes since v5: - Use __ASSUME_RSEQ to detect rseq availability. Changes since v6: - Remove use of __ASSUME_RSEQ. Changes since v7: - Fix incorrect merge with commit d0def09ff6 ("linux: Fix vDSO macros build with time64 interfaces") Changes since v8: - Update patch title. - Add /* RSEQ_SIG */ for #else and #endif. --- sysdeps/unix/sysv/linux/sched_getcpu.c | 22 ++++++++++++++++++++-- 1 file changed, 20 insertions(+), 2 deletions(-) diff --git a/sysdeps/unix/sysv/linux/sched_getcpu.c b/sysdeps/unix/sysv/linux/sched_getcpu.c index c019cfb3cf..c0f992e056 100644 --- a/sysdeps/unix/sysv/linux/sched_getcpu.c +++ b/sysdeps/unix/sysv/linux/sched_getcpu.c @@ -18,10 +18,12 @@ #include <errno.h> #include <sched.h> #include <sysdep.h> +#include <atomic.h> #include <sysdep-vdso.h> +#include <sys/rseq.h> -int -sched_getcpu (void) +static int +vsyscall_sched_getcpu (void) { unsigned int cpu; int r = -1; @@ -32,3 +34,19 @@ sched_getcpu (void) #endif return r == -1 ? r : cpu; } + +#ifdef RSEQ_SIG +int +sched_getcpu (void) +{ + int cpu_id = atomic_load_relaxed (&__rseq_abi.cpu_id); + + return cpu_id >= 0 ? cpu_id : vsyscall_sched_getcpu (); +} +#else /* RSEQ_SIG */ +int +sched_getcpu (void) +{ + return vsyscall_sched_getcpu (); +} +#endif /* RSEQ_SIG */ -- 2.17.1
