From patchwork Fri Nov 2 11:52:59 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mathieu Desnoyers X-Patchwork-Id: 30008 Received: (qmail 107001 invoked by alias); 2 Nov 2018 11:53:11 -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 106876 invoked by uid 89); 2 Nov 2018 11:53:10 -0000 Authentication-Results: sourceware.org; auth=none X-Spam-SWARE-Status: No, score=-26.9 required=5.0 tests=BAYES_00, GIT_PATCH_0, GIT_PATCH_1, GIT_PATCH_2, GIT_PATCH_3, RCVD_IN_DNSWL_NONE, SPF_PASS autolearn=ham version=3.3.2 spammy=Ben, HDKIM-Filter:v2.10.3, H*Ad:D*vnet.ibm.com, H*Ad:D*linux.vnet.ibm.com X-HELO: mail.efficios.com DKIM-Filter: OpenDKIM Filter v2.10.3 mail.efficios.com 94FA52488BB DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=efficios.com; s=default; t=1541159586; bh=ARIXVDaQRUZ7X2dcuyortmQVt+ZsZwR9tFSZPo3/9TE=; h=From:To:Date:Message-Id; b=ZZSYwnaWvaHeKXt1fPCsxFWd4tkBzWSXDVX2O5uWZ/j5MuURmLQG4GBpLDoOUVmxB tHmhi9imrNCjYMmvtsKWDy69aD3p4bSDk8EiXgqK34Oztt/FrE3nferm9K9BA6v4Rl Z8+cst2yRmsOjTnPwWBgQ7WOFsZTW/ssXzJsZr9gd/8yKDu0fICERrSJFUtBntZaDu QzRMaM6XZJnMSXIsSzVrZRIwTYhF/SV/JweutFJgVIxLkyUrTdM+XdAfU6BLTzBfVN ELSuMv5ldHA8ms7AHygqxqKNrQrGQeVs6UOhDb68mgHqhJ6HxKATh/yKRRnn9wjTHx j3/WmM1Hd+mrw== From: Mathieu Desnoyers To: libc-alpha@sourceware.org Cc: Mathieu Desnoyers , Carlos O'Donell , Florian Weimer , Joseph Myers , Szabolcs Nagy , 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 2/2] glibc: sched_getcpu(): use rseq cpu_id TLS on Linux Date: Fri, 2 Nov 2018 07:52:59 -0400 Message-Id: <20181102115259.11383-2-mathieu.desnoyers@efficios.com> In-Reply-To: <20181102115259.11383-1-mathieu.desnoyers@efficios.com> References: <20181102115259.11383-1-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 --- sysdeps/unix/sysv/linux/sched_getcpu.c | 25 +++++++++++++++++++++++-- 1 file changed, 23 insertions(+), 2 deletions(-) diff --git a/sysdeps/unix/sysv/linux/sched_getcpu.c b/sysdeps/unix/sysv/linux/sched_getcpu.c index b69eeda15c..e1a206075c 100644 --- a/sysdeps/unix/sysv/linux/sched_getcpu.c +++ b/sysdeps/unix/sysv/linux/sched_getcpu.c @@ -24,8 +24,8 @@ #endif #include -int -sched_getcpu (void) +static int +vsyscall_sched_getcpu (void) { #ifdef __NR_getcpu unsigned int cpu; @@ -37,3 +37,24 @@ sched_getcpu (void) return -1; #endif } + +#ifdef __NR_rseq +#include + +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