From: john stultz <johnstul@us.ibm.com>
To: Roman Zippel <zippel@linux-m68k.org>
Cc: Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>,
Andrew Morton <akpm@osdl.org>,
linux-kernel@vger.kernel.org
Subject: Re: [RFC] HZ free ntp
Date: Tue, 02 Jan 2007 11:46:24 -0800 [thread overview]
Message-ID: <1167767185.3141.15.camel@localhost> (raw)
In-Reply-To: <200701011929.28546.zippel@linux-m68k.org>
On Mon, 2007-01-01 at 19:29 +0100, Roman Zippel wrote:
> On Wednesday 20 December 2006 02:54, john stultz wrote:
>
> > And here would be the follow on patch (again *untested*) for
> > CONFIG_NO_HZ slowing the time accumulation down to once per second.
>
> Changing it to one creates a potential problem with calling second_overflow().
> It should be called every NTP_INTERVAL_FREQ times, but occasionally it's off
> by one (when xtime is close to a full second and the tick length is different
> from 1sec). At a higher frequency that's not much of a problem, but at one it
> means second_overflow() is occasionally called twice a second or skipped for
> a second. Usually the error should be quite small, but sometimes it can be
> significant.
> So in this case the loop in update_wall_time() should rather look like this:
>
> while (offset >= clock->cycle_interval) {
> ...
> second_overflow();
> while (clock->xtime_nsec >= (u64)NSEC_PER_SEC << clock->shift) {
> clock->xtime_nsec -= (u64)NSEC_PER_SEC << clock->shift;
> xtime.tv_sec++;
> }
> ...
> }
>
> (Also note the change from "if" to "while".)
Ah, good catch! Thank you, I'll add that, retest and send it to akpm.
thanks
-john
next prev parent reply other threads:[~2007-01-02 19:50 UTC|newest]
Thread overview: 85+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-12-05 4:40 -mm merge plans for 2.6.20 Andrew Morton
2006-12-05 4:56 ` Jeff Garzik
2006-12-05 5:41 ` Andrew Morton
2006-12-05 7:04 ` Jens Axboe
2006-12-05 15:00 ` Mark Lord
2006-12-06 19:19 ` Conke Hu
2006-12-06 19:26 ` Randy Dunlap
2006-12-06 19:40 ` Jeff Garzik
2006-12-06 22:36 ` Andrew Morton
2006-12-05 5:14 ` Paul Mackerras
2006-12-05 5:42 ` Andrew Morton
2006-12-05 5:53 ` Nick Piggin
2006-12-05 5:49 ` Nick Piggin
2006-12-05 8:36 ` Gautham R Shenoy
2006-12-05 8:47 ` Peter Zijlstra
2006-12-05 11:06 ` ext2 future [was Re: -mm merge plans for 2.6.20] Pavel Machek
2006-12-05 13:23 ` -mm merge plans for 2.6.20 John W. Linville
2006-12-05 14:27 ` Roman Zippel
2006-12-06 3:46 ` Horst Schirmeier
2006-12-05 16:02 ` Dave Jones
2006-12-12 17:49 ` Dave Jones
2006-12-19 5:20 ` Nick Piggin
2006-12-19 6:44 ` Dave Jones
2006-12-19 7:02 ` Nick Piggin
2007-01-07 17:36 ` page_mapcount(page) went negative Dave Jones
2007-01-10 23:53 ` Nick Piggin
2006-12-05 17:35 ` -mm merge plans for 2.6.20 James Simmons
2006-12-05 18:01 ` Andrew Morton
2006-12-05 18:25 ` James Simmons
2006-12-05 18:37 ` [PATCH] backlight sysfs change to the fbdev drivers James Simmons
2006-12-05 19:43 ` -mm merge plans for 2.6.20 Andrew Morton
2006-12-05 19:59 ` James Simmons
2006-12-05 20:20 ` Andrew Morton
2006-12-05 21:34 ` James Simmons
2006-12-06 23:40 ` Andrew Morton
2006-12-07 14:31 ` James Simmons
2006-12-05 20:40 ` Miguel Ojeda
2006-12-06 14:42 ` James Simmons
2006-12-05 19:18 ` Josef Sipek
2006-12-05 19:21 ` [PATCH 1/2] fsstack: Make fsstack_copy_attr_all copy inode size Josef Sipek
2006-12-05 19:22 ` [PATCH 2/2] fsstack: Fix up ecryptfs's fsstack usage Josef Sipek
2006-12-05 22:28 ` Andrew Morton
2006-12-05 22:38 ` Josef Sipek
2006-12-05 22:49 ` Andrew Morton
2006-12-05 23:16 ` Josef Sipek
2006-12-05 21:00 ` -mm merge plans for 2.6.20 Ingo Molnar
2006-12-05 21:17 ` -mm merge plans for 2.6.20, scheduler bits Ingo Molnar
2006-12-05 20:59 ` Siddha, Suresh B
2006-12-05 21:47 ` Ingo Molnar
2006-12-05 21:29 ` Miguel Ojeda
2006-12-06 2:59 ` -mm merge plans for 2.6.20 Roman Zippel
2006-12-06 4:30 ` Andrew Morton
2006-12-06 8:32 ` Thomas Gleixner
2006-12-06 12:54 ` Roman Zippel
2006-12-06 13:11 ` Ingo Molnar
2006-12-06 14:33 ` Roman Zippel
2006-12-06 15:22 ` Ingo Molnar
2006-12-06 16:42 ` Roman Zippel
2006-12-06 16:58 ` Ingo Molnar
2006-12-06 16:59 ` Ingo Molnar
2006-12-12 20:40 ` [RFC] HZ free ntp john stultz
2006-12-13 9:51 ` Ingo Molnar
2006-12-13 18:48 ` john stultz
2006-12-13 13:47 ` Roman Zippel
2006-12-13 19:19 ` john stultz
2006-12-13 20:40 ` Roman Zippel
2006-12-20 1:32 ` john stultz
2006-12-20 1:54 ` john stultz
2006-12-21 4:26 ` Andrew Morton
2007-01-01 18:29 ` Roman Zippel
2007-01-02 19:46 ` john stultz [this message]
2007-01-02 20:50 ` john stultz
2007-01-06 16:56 ` Roman Zippel
2007-01-22 19:27 ` [patch] HZ-free NTP Ingo Molnar
2007-01-22 19:39 ` Ingo Molnar
2007-01-01 16:27 ` [RFC] HZ free ntp Roman Zippel
2007-01-02 19:42 ` john stultz
2007-01-06 16:46 ` Roman Zippel
2006-12-06 12:33 ` -mm merge plans for 2.6.20 Roman Zippel
2006-12-08 14:09 ` Stephen Smalley
2006-12-08 20:58 ` Andrew Morton
2006-12-10 15:07 ` Mimi Zohar
2006-12-09 9:30 ` Randy Dunlap
2006-12-09 9:44 ` Andrew Morton
2006-12-10 20:12 ` Randy Dunlap
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