Messages in this thread Patch in this message | | | From | Mathieu Desnoyers <> | Subject | [RFC PATCH glibc 10/13] glibc: sched_getcpu(): use rseq cpu_id TLS on Linux (v5) | Date | Fri, 20 Dec 2019 16:36:47 -0500 |
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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@2.40GHz, 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 <mathieu.desnoyers@efficios.com> CC: Carlos O'Donell <carlos@redhat.com> CC: Florian Weimer <fweimer@redhat.com> CC: Joseph Myers <joseph@codesourcery.com> CC: Szabolcs Nagy <szabolcs.nagy@arm.com> CC: Thomas Gleixner <tglx@linutronix.de> CC: Ben Maurer <bmaurer@fb.com> CC: Peter Zijlstra <peterz@infradead.org> CC: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> CC: Boqun Feng <boqun.feng@gmail.com> CC: Will Deacon <will.deacon@arm.com> CC: Dave Watson <davejwatson@fb.com> CC: Paul Turner <pjt@google.com> CC: libc-alpha@sourceware.org CC: linux-kernel@vger.kernel.org CC: linux-api@vger.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. --- ChangeLog.old/ChangeLog.19 | 5 +++++ sysdeps/unix/sysv/linux/sched_getcpu.c | 25 +++++++++++++++++++++++-- 2 files changed, 28 insertions(+), 2 deletions(-)
diff --git a/ChangeLog.old/ChangeLog.19 b/ChangeLog.old/ChangeLog.19 index 9d6496c747..07c6aff585 100644 --- a/ChangeLog.old/ChangeLog.19 +++ b/ChangeLog.old/ChangeLog.19 @@ -1,3 +1,8 @@ +2019-12-17 Mathieu Desnoyers <mathieu.desnoyers@efficios.com> + + * sysdeps/unix/sysv/linux/sched_getcpu.c: use rseq cpu_id TLS on + Linux. + 2019-12-17 Mathieu Desnoyers <mathieu.desnoyers@efficios.com> * NEWS: Add Restartable Sequences feature description. diff --git a/sysdeps/unix/sysv/linux/sched_getcpu.c b/sysdeps/unix/sysv/linux/sched_getcpu.c index 65dd9fdda7..6f24c1db99 100644 --- a/sysdeps/unix/sysv/linux/sched_getcpu.c +++ b/sysdeps/unix/sysv/linux/sched_getcpu.c @@ -18,14 +18,15 @@ #include <errno.h> #include <sched.h> #include <sysdep.h> +#include <atomic.h> #ifdef HAVE_GETCPU_VSYSCALL # define HAVE_VSYSCALL #endif #include <sysdep-vdso.h> -int -sched_getcpu (void) +static int +vsyscall_sched_getcpu (void) { #ifdef __NR_getcpu unsigned int cpu; @@ -37,3 +38,23 @@ sched_getcpu (void) return -1; #endif } + +#ifdef __NR_rseq +#include <sys/rseq.h> +#endif + +#if defined __NR_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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