From patchwork Fri Dec 20 21:36:47 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mathieu Desnoyers X-Patchwork-Id: 37053 Received: (qmail 128406 invoked by alias); 20 Dec 2019 21:38:30 -0000 Mailing-List: contact libc-alpha-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Unsubscribe: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: libc-alpha-owner@sourceware.org Delivered-To: mailing list libc-alpha@sourceware.org Received: (qmail 128332 invoked by uid 89); 20 Dec 2019 21:38:30 -0000 Authentication-Results: sourceware.org; auth=none X-Spam-SWARE-Status: No, score=-25.3 required=5.0 tests=AWL, BAYES_00, GIT_PATCH_0, GIT_PATCH_1, GIT_PATCH_2, GIT_PATCH_3, RCVD_IN_DNSWL_NONE, SPF_PASS autolearn=ham version=3.3.1 spammy=watson, Watson, ben, 3823 X-HELO: mail.efficios.com DKIM-Filter: OpenDKIM Filter v2.10.3 mail.efficios.com 908CA690A46 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=efficios.com; s=default; t=1576877904; bh=/bVnUsGf5G1T0yIcu2lL51PVFsvSJZzRb6jBDRmIQF8=; h=From:To:Date:Message-Id; b=tKN3zjtNK1XqrbY4/FojAITR0EWU4qZjdiRZWxEeTNYk5QGbh/8GQRAMbe3r1Gcvi UmeP6qXi3W6uULCLruh82LnSDQZJt1hvEGB0wri0gI8YfECc+9RiqTUMW4PNa1RO2g b8TaT6cG7SL1u0DBpNMAjslpfwq449b9H3jSTAcPxz0XP81LqPiGJnSBdShzpnJmxG jVHnDP+v2qqn8A1mGpmocA9vBVGa+wdezHhHphEn9OgUce7+utLEGjWtm3xHHn0tEe DF1xjwHIq5OH1X0mAFFtBrvtK5INDIy2Cn6Lha++wWLQZGbKoMO/21M0BNPCPZ2RRX Db/7fvpRCpLnw== From: Mathieu Desnoyers To: Carlos O'Donell Cc: Florian Weimer , Joseph Myers , Szabolcs Nagy , libc-alpha@sourceware.org, Mathieu Desnoyers , Thomas Gleixner , Ben Maurer , Peter Zijlstra , "Paul E. McKenney" , Boqun Feng , Will Deacon , Dave Watson , Paul Turner , linux-kernel@vger.kernel.org, linux-api@vger.kernel.org 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 Message-Id: <20191220213650.11281-11-mathieu.desnoyers@efficios.com> In-Reply-To: <20191220213650.11281-1-mathieu.desnoyers@efficios.com> References: <20191220213650.11281-1-mathieu.desnoyers@efficios.com> 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 CC: Carlos O'Donell CC: Florian Weimer CC: Joseph Myers CC: Szabolcs Nagy CC: Thomas Gleixner CC: Ben Maurer CC: Peter Zijlstra CC: "Paul E. McKenney" CC: Boqun Feng CC: Will Deacon CC: Dave Watson CC: Paul Turner 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 + + * sysdeps/unix/sysv/linux/sched_getcpu.c: use rseq cpu_id TLS on + Linux. + 2019-12-17 Mathieu Desnoyers * 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 #include #include +#include #ifdef HAVE_GETCPU_VSYSCALL # define HAVE_VSYSCALL #endif #include -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 +#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