From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 358A8C433E1 for ; Wed, 15 Jul 2020 05:58:22 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 0019620663 for ; Wed, 15 Jul 2020 05:58:21 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="eDuS4liC"; dkim=fail reason="signature verification failed" (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="Ni/17QdY"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="JmUnuZre" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0019620663 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linutronix.de Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=OKy6/GrNT2paMVy93h7mzzVe4FosTc9DcRitNRinWBQ=; b=eDuS4liCgCCUAsBTA5ax2bKw3 e277c4ri2/kmEQWWDPPF/sv1IQvz/0xUdAqo+YP6Jpjh+zcNHAedRKaDUkdGfpPhNeOHTQs5obrlk 6FReB8ZE/3JO62/D81OcwHPcbILCA2vodxVaSBhKd/DKRQN/ue/uODRJUxmhhjTASPQ+954qVqZra Ece7KSU8w1DlV9raZ/DeLFE/f3ry5WnJjFmuVCt80vaQ3DbF56+2h8Zmi0vPgxciRpiMMuQ0E6vOS ZP50bE5a5TSJB6TiZ9+fhxcPXQNdgEgmaqvTzW2FG6wU6W3WeH3iN6BL7RrPRo5eyCGXkfMMp1A3W vmNv0OYxg==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jvaPX-00070X-WF; Wed, 15 Jul 2020 05:56:56 +0000 Received: from galois.linutronix.de ([193.142.43.55]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1jvaPV-0006zT-El for linux-arm-kernel@lists.infradead.org; Wed, 15 Jul 2020 05:56:54 +0000 Date: Wed, 15 Jul 2020 07:56:50 +0200 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1594792612; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=xEz6zpbt0xsuZlsRzMleqOaAxb08W357YybuYKHG9z8=; b=Ni/17QdYoBFRFr/T8jycotCbAOm4FkXTGT67Yy9HrBndnAE/DL7xUK+o7Fq6gWyV1Hs+DK eu//GM0u77nIcmo35qlqifkHlQHGlU8ZwCJ5zkaaqx3t9ZfATtEgoXv85n3PThNokoqYxa SlbTmZf1v7xQvKZ/xreZZOROSX34u2ukJjC33AhNE/ZUBidQ+a2ELrB2p7zEjhhhhYZ3Z4 ycpiOngX9uws9ImJr4shWoVn+RsgwWv4SVe6gQU23qovvfDlPmpNY5dp4WXpwg9a8QpPrT XOrcReyLtoyESzLcQQkGbqfO8Ogffo7/1ei7WfBjS5nPO6Zd6s9aVvL+Z4Am/g== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1594792612; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=xEz6zpbt0xsuZlsRzMleqOaAxb08W357YybuYKHG9z8=; b=JmUnuZredCRHLaWI1Bu3Wun/oZSKmCV+haaRnFd3KXMuCXaOQkPXJ6KkPHc2B+K4X0nC1D urPjPt/1KTI1hEDg== From: "Ahmed S. Darwish" To: Leo Yan , Peter Zijlstra Subject: Re: [PATCH v2 1/6] sched_clock: Expose struct clock_read_data Message-ID: <20200715055650.GB225020@debian-buster-darwi.lab.linutronix.de> References: <20200715020512.20991-1-leo.yan@linaro.org> <20200715020512.20991-2-leo.yan@linaro.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200715020512.20991-2-leo.yan@linaro.org> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200715_015653_620076_02AF1053 X-CRM114-Status: UNSURE ( 9.45 ) X-CRM114-Notice: Please train this message. X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Alexander Shishkin , Will Deacon , Adrian Hunter , Arnaldo Carvalho de Melo , linux-kernel@vger.kernel.org, Paul Cercueil , Ingo Molnar , Catalin Marinas , Namhyung Kim , Thomas Gleixner , jogness@linutronix.de, Jiri Olsa , "Ben Dooks \(Codethink\)" , linux-arm-kernel@lists.infradead.org, Kan Liang Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, Jul 15, 2020 at 10:05:07AM +0800, Leo Yan wrote: > From: Peter Zijlstra > ... > > Provide struct clock_read_data and two (seqcount) helpers so that > architectures (arm64 in specific) can expose the numbers to userspace. > ... > > +struct clock_read_data *sched_clock_read_begin(unsigned int *seq) > +{ > + *seq = raw_read_seqcount(&cd.seq); > + return cd.read_data + (*seq & 1); > +} > + ... Hmm, this seqcount_t is actually a latch seqcount. I know the original code also used raw_read_seqcount(), but while at it, let's use the proper read API for seqcount_t latchers: raw_read_seqcount_latch(). raw_read_seqcount_latch() has no read memory barrier though, and a suspicious claim that READ_ONCE() pairs with an smp_wmb() (??). But if its implementation is wrong, let's fix it there instead. Thanks, -- Ahmed S. Darwish Linutronix GmbH _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel