Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760519AbXIKWgp (ORCPT ); Tue, 11 Sep 2007 18:36:45 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754773AbXIKWgi (ORCPT ); Tue, 11 Sep 2007 18:36:38 -0400 Received: from www.osadl.org ([213.239.205.134]:48618 "EHLO mail.tglx.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751462AbXIKWgh (ORCPT ); Tue, 11 Sep 2007 18:36:37 -0400 Subject: [PATCH] timekeeping: Prevent time going backwards on resume From: Thomas Gleixner To: Andrew Morton Cc: LKML , john stultz , Ingo Molnar , Marcelo Tosatti Content-Type: text/plain Date: Wed, 12 Sep 2007 00:36:34 +0200 Message-Id: <1189550194.5235.99.camel@chaos> Mime-Version: 1.0 X-Mailer: Evolution 2.11.92 (2.11.92-1.fc8) Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2857 Lines: 75 Timekeeping resume adjusts xtime by adding the slept time in seconds and resets the reference value of the clock source (clock->cycle_last). clock->cycle last is used to calculate the delta between the last xtime update and the readout of the clock source in __get_nsec_offset(). xtime plus the offset is the current time. The resume code ignores the delta which had already elapsed between the last xtime update and the actual time of suspend. If the suspend time is short, then we can see time going backwards on resume. Suspend: offs_s = clock->read() - clock->cycle_last; now = xtime + offs_s; timekeeping_suspend_time = read_rtc(); Resume: sleep_time = read_rtc() - timekeeping_suspend_time; xtime.tv_sec += sleep_time; clock->cycle_last = clock->read(); offs_r = clock->read() - clock->cycle_last; now = xtime + offs_r; if sleep_time_seconds == 0 and offs_r < offs_s, then time goes backwards. Fix this by storing the offset from the last xtime update and add it to xtime during resume, when we reset clock->cycle_last: sleep_time = read_rtc() - timekeeping_suspend_time; xtime.tv_sec += sleep_time; xtime += offs_s; /* Fixup xtime offset at suspend time */ clock->cycle_last = clock->read(); offs_r = clock->read() - clock->cycle_last; now = xtime + offs_r; Thanks to Marcelo for tracking this down on the OLPC and providing the necessary details to analyze the root cause. Signed-off-by: Thomas Gleixner --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -280,6 +280,8 @@ void __init timekeeping_init(void) static int timekeeping_suspended; /* time in seconds when suspend began */ static unsigned long timekeeping_suspend_time; +/* xtime offset when we went into suspend */ +static s64 timekeeping_suspend_offset; /** * timekeeping_resume - Resumes the generic timekeeping subsystem. @@ -305,6 +307,8 @@ static int timekeeping_resume(struct sys_device *dev) wall_to_monotonic.tv_sec -= sleep_length; total_sleep_time += sleep_length; } + /* Make sure that we have the correct xtime reference */ + timespec_add_ns(&xtime, timekeeping_suspend_offset); /* re-base the last cycle value */ clock->cycle_last = clocksource_read(clock); clock->error = 0; @@ -326,6 +330,8 @@ static int timekeeping_suspend(struct sys_device *dev, pm_message_t state) unsigned long flags; write_seqlock_irqsave(&xtime_lock, flags); timekeeping_suspended = 1; + /* Get the current xtime offset */ + timekeeping_suspend_offset = __get_nsec_offset(); timekeeping_suspend_time = read_persistent_clock(); write_sequnlock_irqrestore(&xtime_lock, flags); - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/