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) Signed-off-by: Mathieu Desnoyers <[email protected]> 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: Dave Watson <[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. --- sysdeps/unix/sysv/linux/sched_getcpu.c | 27 ++++++++++++++++++++++++-- 1 file changed, 25 insertions(+), 2 deletions(-) diff --git a/sysdeps/unix/sysv/linux/sched_getcpu.c b/sysdeps/unix/sysv/linux/sched_getcpu.c index fb0d317f83..f9466c3b22 100644 --- a/sysdeps/unix/sysv/linux/sched_getcpu.c +++ b/sysdeps/unix/sysv/linux/sched_getcpu.c @@ -24,8 +24,8 @@ #endif #include <sysdep-vdso.h> -int -sched_getcpu (void) +static int +vsyscall_sched_getcpu (void) { #ifdef __NR_getcpu unsigned int cpu; @@ -37,3 +37,26 @@ sched_getcpu (void) return -1; #endif } + +#ifdef __NR_rseq +#include <sys/rseq.h> +#endif + +#if defined __NR_rseq && defined RSEQ_SIG +extern __attribute__ ((tls_model ("initial-exec"))) +__thread volatile struct rseq __rseq_abi; + +int +sched_getcpu (void) +{ + int cpu_id = __rseq_abi.cpu_id; + + return cpu_id >= 0 ? cpu_id : vsyscall_sched_getcpu (); +} +#else +int +sched_getcpu (void) +{ + return vsyscall_sched_getcpu (); +} +#endif -- 2.17.1
