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: AS17314 8.43.84.0/22 X-Spam-Status: No, score=-4.2 required=3.0 tests=AWL,BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,MAILING_LIST_MULTI, SPF_HELO_PASS,SPF_PASS shortcircuit=no autolearn=ham autolearn_force=no version=3.4.2 Received: from sourceware.org (server2.sourceware.org [8.43.85.97]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by dcvr.yhbt.net (Postfix) with ESMTPS id D70861F9E0 for ; Tue, 28 Apr 2020 17:15:24 +0000 (UTC) Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id 1C1193851C2D; Tue, 28 Apr 2020 17:15:24 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 1C1193851C2D DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sourceware.org; s=default; t=1588094124; bh=0smAkb6cp0p+RuLi71ihxVXx+NcGlOLwapAddILSwQ4=; h=To:Subject:Date:In-Reply-To:References:List-Id:List-Unsubscribe: List-Archive:List-Post:List-Help:List-Subscribe:From:Reply-To:Cc: From; b=n+SMKVKdDVEb9GEpRz9OBorvMVJAjywNDzijieoxS68OmqMFMtO30Vm2PrYmowbuf xG2gk/bUEF2PpkcSptoezi6x7Urmiqcbx2r2UajKtK+GfVaB71Qw4dFajlVjtL985x Rle9ue59kq3ZyN5BtpBG1ZgroOGAnAttFdKKnFnA= Received: from mail.efficios.com (mail.efficios.com [167.114.26.124]) by sourceware.org (Postfix) with ESMTPS id 339A5385DC32 for ; Tue, 28 Apr 2020 17:15:21 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 339A5385DC32 Received: from localhost (localhost [127.0.0.1]) by mail.efficios.com (Postfix) with ESMTP id C162D27E927; Tue, 28 Apr 2020 13:15:20 -0400 (EDT) Received: from mail.efficios.com ([127.0.0.1]) by localhost (mail03.efficios.com [127.0.0.1]) (amavisd-new, port 10032) with ESMTP id m-OwioVHNQqU; Tue, 28 Apr 2020 13:15:20 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by mail.efficios.com (Postfix) with ESMTP id 5589727E926; Tue, 28 Apr 2020 13:15:20 -0400 (EDT) DKIM-Filter: OpenDKIM Filter v2.10.3 mail.efficios.com 5589727E926 X-Virus-Scanned: amavisd-new at efficios.com Received: from mail.efficios.com ([127.0.0.1]) by localhost (mail03.efficios.com [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id NdISAkAmPADx; Tue, 28 Apr 2020 13:15:20 -0400 (EDT) Received: from localhost.localdomain (192-222-181-218.qc.cable.ebox.net [192.222.181.218]) by mail.efficios.com (Postfix) with ESMTPSA id 128FC27E91B; Tue, 28 Apr 2020 13:15:20 -0400 (EDT) To: Carlos O'Donell Subject: [RFC PATCH glibc 2/3] glibc: sched_getcpu(): use rseq cpu_id TLS on Linux (v7) Date: Tue, 28 Apr 2020 13:15:12 -0400 Message-Id: <20200428171513.22926-2-mathieu.desnoyers@efficios.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20200428171513.22926-1-mathieu.desnoyers@efficios.com> References: <20200428171513.22926-1-mathieu.desnoyers@efficios.com> X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , From: Mathieu Desnoyers via Libc-alpha Reply-To: Mathieu Desnoyers Cc: libc-alpha@sourceware.org, linux-api@vger.kernel.org, Boqun Feng , Will Deacon , linux-kernel@vger.kernel.org, Peter Zijlstra , Ben Maurer , Mathieu Desnoyers , Thomas Gleixner , "Paul E. McKenney" , Paul Turner , Joseph Myers Errors-To: libc-alpha-bounces@sourceware.org Sender: "Libc-alpha" 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) 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: 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. Changes since v5: - Use __ASSUME_RSEQ to detect rseq availability. Changes since v6: - Remove use of __ASSUME_RSEQ. --- sysdeps/unix/sysv/linux/sched_getcpu.c | 27 ++++++++++++++++++++++++-- 1 file changed, 25 insertions(+), 2 deletions(-) diff --git a/sysdeps/unix/sysv/linux/sched_getcpu.c b/sysdeps/unix/sysv/linux/sched_getcpu.c index c019cfb3cf..2269c4f2bd 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 +37,21 @@ sched_getcpu (void) #endif return r == -1 ? r : cpu; } + +#include + +#ifdef 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