From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759051AbZBMDCT (ORCPT ); Thu, 12 Feb 2009 22:02:19 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752371AbZBMDCI (ORCPT ); Thu, 12 Feb 2009 22:02:08 -0500 Received: from e39.co.us.ibm.com ([32.97.110.160]:33605 "EHLO e39.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751127AbZBMDCF (ORCPT ); Thu, 12 Feb 2009 22:02:05 -0500 Subject: [PATCH][RFC] Apply NTP frequency/tick changes immediately. From: john stultz To: Roman Zippel Cc: Clark Williams , lkml Content-Type: text/plain Date: Thu, 12 Feb 2009 19:02:01 -0800 Message-Id: <1234494121.7042.14.camel@localhost.localdomain> Mime-Version: 1.0 X-Mailer: Evolution 2.22.3.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hey Roman, It was brought to my attention that since the GENERIC_TIME changes landed, the adjtimex behavior changed for struct timex.tick and .freq changes. When the tick or freq value is set, we adjust the tick_length_base in ntp_update_frequency(). However, this new value doesn't get applied to tick_length until the next second (via second_overflow). This means some applications that do quick time tweaking do not see the requested change made as quickly as expected. Looking at the code, it doesn't seem like it would be too hard to immediately apply the change to the tick_length value, so its changed in the following NTP_INTERVAL, which this patch does. I've run a few tests with this change, and ntpd still functions fine. I do however note that the drift value for my test system changed from ~170ppm to ~18ppm, which I didn't quite expect, and needs some additional research. Anyway, I just wanted to see if you had any thoughts on this sort of change. thanks -john Apply NTP tick/frequency adjustments immediately instead of waiting for the next second to pass. Signed-off-by: John Stultz diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c index f5f793d..9fd0d15 100644 --- a/kernel/time/ntp.c +++ b/kernel/time/ntp.c @@ -51,6 +51,7 @@ static long ntp_tick_adj; static void ntp_update_frequency(void) { + u64 old_tick_length_base = tick_length_base; u64 second_length = (u64)(tick_usec * NSEC_PER_USEC * USER_HZ) << NTP_SCALE_SHIFT; second_length += (s64)ntp_tick_adj << NTP_SCALE_SHIFT; @@ -60,6 +61,11 @@ static void ntp_update_frequency(void) tick_nsec = div_u64(second_length, HZ) >> NTP_SCALE_SHIFT; tick_length_base = div_u64(tick_length_base, NTP_INTERVAL_FREQ); + + /* Don't wait for the next second_overflow, apply + * the change to the tick length immediately + */ + tick_length += tick_length_base - old_tick_length_base; } static void ntp_update_offset(long offset)