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=-9.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham 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 70CCAC76188 for ; Mon, 22 Jul 2019 10:34:10 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 469E221985 for ; Mon, 22 Jul 2019 10:34:10 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="H8QCCkn0" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 469E221985 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-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=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Message-Id:Date:Subject:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=9OV3xeTJIza/o/QnElCaSu5XFiHY4IDPE2lzUW+USYk=; b=H8QCCkn0s+b5Nl 9WokjVnI/H38juoPHwp/YdD1FZn7YxdAryL/hqwv3ZScNz8rt7qb1xDOLkjIhzCp00agS1wCVQ8kX f/aGCDRvg3q/b2BLVpm3KU/rfG2pFK/t0R7kiSkm+r8Ywd8Y5aqYpRt36+IEf9o4awHRQr41czePB abwrqn+G8amcacylb7tW8M8xO2UDvUeTv19z1+QuOSCM+xqisxkyGNWRl5sxK/7ecCV8xu5tdaWCl NEq8EypDjiHKOsTt/KjpzYl+OV40FuMbzFkRodQwHPmppo19qHiWf5poWg3ej2QkCc7tfuf1KIRgG DTONXONLlLGqcyrUD8yA==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1hpVdv-0003Wc-3O; Mon, 22 Jul 2019 10:34:07 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1hpVdY-00038K-PI for linux-arm-kernel@lists.infradead.org; Mon, 22 Jul 2019 10:33:46 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id E27DD1576; Mon, 22 Jul 2019 03:33:43 -0700 (PDT) Received: from filthy-habits.cambridge.arm.com (filthy-habits.cambridge.arm.com [10.1.197.61]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 7347E3F71A; Mon, 22 Jul 2019 03:33:42 -0700 (PDT) From: Marc Zyngier To: Thomas Gleixner , John Stultz , Pavel Tatashin , Petr Mladek , Sergey Senozhatsky , Steven Rostedt , Will Deacon , Catalin Marinas , Mark Rutland Subject: [PATCH 2/3] sched/clock: Allow sched_clock to inherit timestamp_clock epoch Date: Mon, 22 Jul 2019 11:33:29 +0100 Message-Id: <20190722103330.255312-3-marc.zyngier@arm.com> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190722103330.255312-1-marc.zyngier@arm.com> References: <20190722103330.255312-1-marc.zyngier@arm.com> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190722_033344_863178_F85529F1 X-CRM114-Status: GOOD ( 13.80 ) 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: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org Now that we can let an architecture override the timestamping function, it becomes desirable to ensure that, should the architecture code switch its timestamping code to sched_clock once it has been registered, the sched_clock inherits the timestamp value as its new epoch. This ensures that the time stamps are continuous and that there is no jitter other than that introduced by the lack of quality of the timestamping clock. Signed-off-by: Marc Zyngier --- kernel/time/sched_clock.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/kernel/time/sched_clock.c b/kernel/time/sched_clock.c index 142b07619918..ee1bd449ec81 100644 --- a/kernel/time/sched_clock.c +++ b/kernel/time/sched_clock.c @@ -192,6 +192,16 @@ sched_clock_register(u64 (*read)(void), int bits, unsigned long rate) new_epoch = read(); cyc = cd.actual_read_sched_clock(); ns = rd.epoch_ns + cyc_to_ns((cyc - rd.epoch_cyc) & rd.sched_clock_mask, rd.mult, rd.shift); + + /* + * If the architecture has a timestamp clock, and this is the + * first time we register a new sched_clock, use the timestamp + * clock as the epoch. + */ + if (IS_ENABLED(CONFIG_ARCH_HAS_TIMESTAMP_CLOCK) && + unlikely(cd.actual_read_sched_clock == jiffy_sched_clock_read)) + ns = timestamp_clock(); + cd.actual_read_sched_clock = read; rd.read_sched_clock = read; -- 2.20.1 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel