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Date: Thu, 19 Mar 2020 10:41:07 -0400 From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com> To: Carlos O'Donell <carlos@...hat.com> Cc: Florian Weimer <fweimer@...hat.com>, Joseph Myers <joseph@...esourcery.com>, Szabolcs Nagy <szabolcs.nagy@....com>, libc-alpha@...rceware.org, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Thomas Gleixner <tglx@...utronix.de>, Ben Maurer <bmaurer@...com>, Peter Zijlstra <peterz@...radead.org>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, Boqun Feng <boqun.feng@...il.com>, Will Deacon <will.deacon@....com>, Dave Watson <davejwatson@...com>, Paul Turner <pjt@...gle.com>, linux-kernel@...r.kernel.org, linux-api@...r.kernel.org Subject: [RFC PATCH glibc 5/8] glibc: sched_getcpu(): use rseq cpu_id TLS on Linux (v6) 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 v3@...0GHz, 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) * sysdeps/unix/sysv/linux/sched_getcpu.c: use rseq cpu_id TLS on Linux. Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com> CC: Carlos O'Donell <carlos@...hat.com> CC: Florian Weimer <fweimer@...hat.com> CC: Joseph Myers <joseph@...esourcery.com> CC: Szabolcs Nagy <szabolcs.nagy@....com> CC: Thomas Gleixner <tglx@...utronix.de> CC: Ben Maurer <bmaurer@...com> CC: Peter Zijlstra <peterz@...radead.org> CC: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> CC: Boqun Feng <boqun.feng@...il.com> CC: Will Deacon <will.deacon@....com> CC: Dave Watson <davejwatson@...com> CC: Paul Turner <pjt@...gle.com> CC: libc-alpha@...rceware.org CC: linux-kernel@...r.kernel.org CC: linux-api@...r.kernel.org --- 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. --- sysdeps/unix/sysv/linux/sched_getcpu.c | 30 ++++++++++++++++++++++++-- 1 file changed, 28 insertions(+), 2 deletions(-) diff --git a/sysdeps/unix/sysv/linux/sched_getcpu.c b/sysdeps/unix/sysv/linux/sched_getcpu.c index c019cfb3cf..4f2c5c4b1a 100644 --- a/sysdeps/unix/sysv/linux/sched_getcpu.c +++ b/sysdeps/unix/sysv/linux/sched_getcpu.c @@ -18,10 +18,16 @@ #include <errno.h> #include <sched.h> #include <sysdep.h> +#include <atomic.h> #include <sysdep-vdso.h> +#include <kernel-features.h> -int -sched_getcpu (void) +#ifdef HAVE_GETCPU_VSYSCALL +# define HAVE_VSYSCALL +#endif + +static int +vsyscall_sched_getcpu (void) { unsigned int cpu; int r = -1; @@ -32,3 +38,23 @@ sched_getcpu (void) #endif return r == -1 ? r : cpu; } + +#ifdef __ASSUME_RSEQ +#include <sys/rseq.h> +#endif + +#if defined __ASSUME_RSEQ && defined 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 +int +sched_getcpu (void) +{ + return vsyscall_sched_getcpu (); +} +#endif -- 2.17.1
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