From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756952Ab2GMFYH (ORCPT ); Fri, 13 Jul 2012 01:24:07 -0400 Received: from e35.co.us.ibm.com ([32.97.110.153]:58123 "EHLO e35.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755472Ab2GMFYE (ORCPT ); Fri, 13 Jul 2012 01:24:04 -0400 From: John Stultz To: Linux Kernel Cc: John Stultz , Ingo Molnar , Peter Zijlstra , Richard Cochran , Prarit Bhargava , Thomas Gleixner , John Stultz Subject: [PATCH 7/8] time: Move xtime_nsec adjustment underflow handling timekeeping_adjust Date: Fri, 13 Jul 2012 01:21:56 -0400 Message-Id: <1342156917-25092-8-git-send-email-john.stultz@linaro.org> X-Mailer: git-send-email 1.7.9.5 In-Reply-To: <1342156917-25092-1-git-send-email-john.stultz@linaro.org> References: <1342156917-25092-1-git-send-email-john.stultz@linaro.org> X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12071305-6148-0000-0000-0000079F0AB7 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org When we make adjustments speeding up the clock, its possible for xtime_nsec to underflow. We already handle this properly, but we do so from update_wall_time() instead of the more logical timekeeping_adjust(), where the possible underflow actually occurs. Thus, move the correction logic to the timekeeping_adjust, which is the function that causes the issue. Making update_wall_time() more readable. CC: Ingo Molnar CC: Peter Zijlstra CC: Richard Cochran CC: Prarit Bhargava CC: Thomas Gleixner Signed-off-by: John Stultz --- kernel/time/timekeeping.c | 42 +++++++++++++++++++++--------------------- 1 file changed, 21 insertions(+), 21 deletions(-) diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index dd119355..4b76432 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -987,6 +987,27 @@ static void timekeeping_adjust(s64 offset) timekeeper.xtime_nsec -= offset; timekeeper.ntp_error -= (interval - offset) << timekeeper.ntp_error_shift; + + /* + * It may be possible that when we entered this function, xtime_nsec + * was very small. Further, if we're slightly speeding the clocksource + * in the code above, its possible the required corrective factor to + * xtime_nsec could cause it to underflow. + * + * Now, since we already accumulated the second, cannot simply roll + * the accumulated second back, since the NTP subsystem has been + * notified via second_overflow. So instead we push xtime_nsec forward + * by the amount we underflowed, and add that amount into the error. + * + * We'll correct this error next time through this function, when + * xtime_nsec is not as small. + */ + if (unlikely((s64)timekeeper.xtime_nsec < 0)) { + s64 neg = -(s64)timekeeper.xtime_nsec; + timekeeper.xtime_nsec = 0; + timekeeper.ntp_error += neg << timekeeper.ntp_error_shift; + } + } @@ -1112,27 +1133,6 @@ static void update_wall_time(void) /* correct the clock when NTP error is too big */ timekeeping_adjust(offset); - /* - * Since in the loop above, we accumulate any amount of time - * in xtime_nsec over a second into xtime.tv_sec, its possible for - * xtime_nsec to be fairly small after the loop. Further, if we're - * slightly speeding the clocksource up in timekeeping_adjust(), - * its possible the required corrective factor to xtime_nsec could - * cause it to underflow. - * - * Now, we cannot simply roll the accumulated second back, since - * the NTP subsystem has been notified via second_overflow. So - * instead we push xtime_nsec forward by the amount we underflowed, - * and add that amount into the error. - * - * We'll correct this error next time through this function, when - * xtime_nsec is not as small. - */ - if (unlikely((s64)timekeeper.xtime_nsec < 0)) { - s64 neg = -(s64)timekeeper.xtime_nsec; - timekeeper.xtime_nsec = 0; - timekeeper.ntp_error += neg << timekeeper.ntp_error_shift; - } /* * Store only full nanoseconds into xtime_nsec after rounding -- 1.7.9.5