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=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 56BA7C76188 for ; Mon, 22 Jul 2019 10:33:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 36DEF21911 for ; Mon, 22 Jul 2019 10:33:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729684AbfGVKdr (ORCPT ); Mon, 22 Jul 2019 06:33:47 -0400 Received: from foss.arm.com ([217.140.110.172]:35440 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729575AbfGVKdo (ORCPT ); Mon, 22 Jul 2019 06:33:44 -0400 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 Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org 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 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.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