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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 CEF86C433E0 for ; Mon, 18 May 2020 13:01:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A9331207D3 for ; Mon, 18 May 2020 13:01:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727822AbgERNB1 convert rfc822-to-8bit (ORCPT ); Mon, 18 May 2020 09:01:27 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43808 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726726AbgERNB1 (ORCPT ); Mon, 18 May 2020 09:01:27 -0400 Received: from Galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 73116C061A0C for ; Mon, 18 May 2020 06:01:27 -0700 (PDT) Received: from p5de0bf0b.dip0.t-ipconnect.de ([93.224.191.11] helo=nanos.tec.linutronix.de) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1jafOY-0001kn-0i; Mon, 18 May 2020 15:01:26 +0200 Received: by nanos.tec.linutronix.de (Postfix, from userid 1000) id 5897E100606; Mon, 18 May 2020 15:01:25 +0200 (CEST) From: Thomas Gleixner To: Pali =?utf-8?Q?Roh=C3=A1r?= Cc: linux-kernel@vger.kernel.org Subject: Re: Missing CLOCK_BOOTTIME_RAW? In-Reply-To: <20200518124902.yuw2rtmjndi7nbd2@pali> References: <20200508213122.f7srcd2gnduamtvs@pali> <87zhah4evs.fsf@nanos.tec.linutronix.de> <20200518111103.sj73h5j3r75zv2wp@pali> <87ftbxxz55.fsf@nanos.tec.linutronix.de> <20200518113522.y6sj7ypunsu6pi3s@pali> <87d071xwxv.fsf@nanos.tec.linutronix.de> <20200518124902.yuw2rtmjndi7nbd2@pali> Date: Mon, 18 May 2020 15:01:25 +0200 Message-ID: <87a725xuqi.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Pali Rohár writes: > On Monday 18 May 2020 14:13:48 Thomas Gleixner wrote: >> Of course not, but the kernel relies on that application behaving >> sanely. If it does not then the time stamps you are complaining about >> are the least of your worries. > > I do not thing it is too bad... When I needed to deal in userspace with > time/date/clock I just needed either "current time in UTC" to show it to > user (possible in different timezone and pretty formatted) or I needed > "timestamp since some epoch" suitable for measuring time differences. > > For first case I used CLOCK_REALTIME and for second case I used > CLOCK_MONOTONIC_RAW (as it was not affected by adjtime()). > > And I would like to know, it is correct to use these two clocks in those > situations? It's your choice to do so. I prefer CLOCK_MONOTONIC simply because it's in human understandable units and not some assumed frequency. > Anyway, what would happen with CLOCK_BOOTTIME when during suspend is > that external RTC source shifted back? Is kernel guarantee that > CLOCK_BOOTTIME is always monotonic even in this case? If the RTC delta is negative, then it's ignored, i.e. 0 sleep time injected. Thanks, tglx