From patchwork Wed Jan 8 14:58:48 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mathieu Desnoyers X-Patchwork-Id: 37252 Received: (qmail 14260 invoked by alias); 8 Jan 2020 14:59:29 -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 14153 invoked by uid 89); 8 Jan 2020 14:59:29 -0000 Authentication-Results: sourceware.org; auth=none X-Spam-SWARE-Status: No, score=-25.6 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=0.8, 1810, 1815 X-HELO: mail.efficios.com DKIM-Filter: OpenDKIM Filter v2.10.3 mail.efficios.com C00A76959CD DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=efficios.com; s=default; t=1578495562; bh=csmXiMR894cheYBJKST2fVas13SXJ+OppF5lHATVWIs=; h=From:To:Date:Message-Id; b=kF/rFIjYU6pzhYQQoiLv1a+lDJ6XnzLG4nfCeapqzamCqpKamE9E1saWOkr8+ZRxU sIPdkjoVurzsbTmhArqg857rMRGLSUuo4hb6UAJLKqgJY/lHV37DKSxmDxZWeU+z+i lkTYGYmM8U9d3RtKbWnjokQ5ciDVv1l+P3xGKxuSoAekD8OC6POlVji7FWUaATH2xh 34YSL/FM4bvOXFXbl/KzP4vptXcLYW4UMfl23YK0Y6ZsxdJvzxI8XX3XTRBUq44IN5 JTBCnLyWAeYGFvDAOrOCoPSGV9I1mcZ/V9dbsXyYgp000jPpFnagA/aCmEKuoaZfgr tqKQzFhQiG9Eg== 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 5/8] glibc: sched_getcpu(): use rseq cpu_id TLS on Linux (v5) Date: Wed, 8 Jan 2020 09:58:48 -0500 Message-Id: <20200108145851.13594-6-mathieu.desnoyers@efficios.com> In-Reply-To: <20200108145851.13594-1-mathieu.desnoyers@efficios.com> References: <20200108145851.13594-1-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) * sysdeps/unix/sysv/linux/sched_getcpu.c: use rseq cpu_id TLS on Linux. 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. --- sysdeps/unix/sysv/linux/sched_getcpu.c | 29 ++++++++++++++++++++++++-- 1 file changed, 27 insertions(+), 2 deletions(-) diff --git a/sysdeps/unix/sysv/linux/sched_getcpu.c b/sysdeps/unix/sysv/linux/sched_getcpu.c index c019cfb3cf..6d3541333d 100644 --- a/sysdeps/unix/sysv/linux/sched_getcpu.c +++ b/sysdeps/unix/sysv/linux/sched_getcpu.c @@ -18,10 +18,15 @@ #include #include #include +#include #include -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 +37,23 @@ sched_getcpu (void) #endif return r == -1 ? r : cpu; } + +#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