From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on dcvr.yhbt.net X-Spam-Level: X-Spam-ASN: AS31976 209.132.180.0/23 X-Spam-Status: No, score=-4.1 required=3.0 tests=AWL,BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_MED,RCVD_IN_MSPIKE_H3, RCVD_IN_MSPIKE_WL,SPF_HELO_PASS,SPF_PASS shortcircuit=no autolearn=ham autolearn_force=no version=3.4.2 Received: from sourceware.org (server1.sourceware.org [209.132.180.131]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dcvr.yhbt.net (Postfix) with ESMTPS id 2D7F71F463 for ; Mon, 6 Jan 2020 16:07:01 +0000 (UTC) DomainKey-Signature: a=rsa-sha1; c=nofws; d=sourceware.org; h=list-id :list-unsubscribe:list-subscribe:list-archive:list-post :list-help:sender:from:to:cc:subject:date:message-id:in-reply-to :references; q=dns; s=default; b=mrn8SMgjEcpUdsuAJlGkI6k2vAb5Pqm LjMoZEpdExh6CSHjpq8N388cn1L6YpVi9PhWdvL2q5oVL2K500RZ3U2SY+BRMk+R 5DPnGwH+CEeYYI7Q4HDdzsc0BpBZQaioYOzN3l19q0v0eLn5C9ZjiBTCCXVcKc8p +BAcoaK/NhdU= DKIM-Signature: v=1; a=rsa-sha1; c=relaxed; d=sourceware.org; h=list-id :list-unsubscribe:list-subscribe:list-archive:list-post :list-help:sender:from:to:cc:subject:date:message-id:in-reply-to :references; s=default; bh=+3Kg2mkyRgVAxoHOKP/VW8isgjM=; b=S4Le5 cQx2df+rglZoUpqzSnnyOGKr9xB7JiecMz0lL8/6PCLiN8hgfneYkf8i1kGlBb6v t/yUfvesyLlZ/PpoStUXa3szwCC2xRETUfBIeAUccRMsdbMrf0xXnqNwxSvRQJTz axZo0Hpet4T25cUhnRBr1nV5df6D6V7HCfjDeg= Received: (qmail 15648 invoked by alias); 6 Jan 2020 16:06:57 -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 Received: (qmail 15602 invoked by uid 89); 6 Jan 2020 16:06:56 -0000 Authentication-Results: sourceware.org; auth=none X-HELO: mail.efficios.com DKIM-Filter: OpenDKIM Filter v2.10.3 mail.efficios.com 983511EA1D4 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=efficios.com; s=default; t=1578326241; bh=V01sGTkdCO7SqIi8D+mEDAjTS4ndQ4TnKwFDOpxXqBA=; h=From:To:Date:Message-Id; b=uG6SHO5pZWLZyzrvJ+miQCWNOw3+othcNc8D+G11B4x+s8a/NnE40NAwnCnPV9a1a nMf4dVo1cgWqrNkk2Ty+wUL0fsuLyYCrFPPOybJbz83WicNS/dAqIxx9W43qbX2Ly6 4LfJwkED7+3LD8PyOtRtVs73tO2dX1CNsir7zitNaoOWXcOH8cwoMY5Q8H3VFb2Bgp zIwjMW2T8C2G3csESuMWfzfArC9UFprrDr1lKmxmI0Gw/PfOQgRRF6n9LjH3gtxx2v s1xlFESfthQEnrMzF+E43fzxYaAeLY5kP+hqP9eQ/CE13r00TjfkoetsarAzHnVSQw GTHE4UZALHTsg== 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: Mon, 6 Jan 2020 10:57:10 -0500 Message-Id: <20200106155713.397-11-mathieu.desnoyers@efficios.com> In-Reply-To: <20200106155713.397-1-mathieu.desnoyers@efficios.com> References: <20200106155713.397-1-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 | 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 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 -- 2.17.1