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From: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
To: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Subject: Re: [PATCH] nohz: add missing handling of clocksource watchdog
Date: Mon, 8 Dec 2008 01:24:37 +0100
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Cc: "R. J. Wysocki" <Rafal.Wysocki@fuw.edu.pl>,
       Thomas Gleixner <tglx@linutronix.de>,
       Lars Winterfeld <lars.winterfeld@tu-ilmenau.de>,
       linux-kernel@vger.kernel.org
References: <200812080015.22793.bzolnier@gmail.com> <200812080036.59506.Rafal.Wysocki@fuw.edu.pl> <493C60E3.7070303@ru.mvista.com>
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On Monday 08 December 2008, Sergei Shtylyov wrote:> Hello.> > R. J. Wysocki wrote:> > On Monday, 8 of December 2008, Bartlomiej Zolnierkiewicz wrote:> >   > >> Fixes "Clocksource tsc unstable (delta = -974982308 ns)" problem.> >>     > >> > Where can I find the description of the problem?> >   > >    Kernel.org bug #10216 (it's not about this issue though).
Looking back at bug #10216 the patch is unlikely to help Lars' systemsince it doesn't use nohz and there are also warnings about unsyncedTSCs (I just don't know why not for 2.6.27-rc kernels)... > > Rafael> >> >   > >> [ IDE was unlucky to be initialized at the same time that> >>   clocksource watchdog triggers and was blamed for the issue. ]> >>     > >    I think it might well have been blamed correctly -- the clocksource > watchdog timer gets run every half second.
AFAICS this is a special one for measuring stability of the clocksourceonly -- by comparing the value returned by a given clocksource with thereference clocksource.  Normal drivers have no bussiness there...
Anyway I forgot to add that it fixes the issue for me under QEMU (on mylaptop TSC is unstable due to halts in idle) and it could be as well QEMU'soddity (although it looks like a legit kernel problem).  v2 of the patchbelow (updated patch description).
From: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>Subject: [PATCH v2] nohz: add missing handling of clocksource watchdog
Fixes "Clocksource tsc unstable (delta = -974982308 ns)" problemunder QEMU.
Cc: Sergei Shtylyov <sshtylyov@ru.mvista.com>Cc: Lars Winterfeld <lars.winterfeld@tu-ilmenau.de>Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>--- kernel/time/tick-sched.c |    2 ++ 1 file changed, 2 insertions(+)
Index: b/kernel/time/tick-sched.c===================================================================--- a/kernel/time/tick-sched.c+++ b/kernel/time/tick-sched.c@@ -21,6 +21,7 @@ #include <linux/sched.h> #include <linux/tick.h> #include <linux/module.h>+#include <linux/clocksource.h>  #include <asm/irq_regs.h> @@ -153,6 +154,7 @@ void tick_nohz_update_jiffies(void) 	local_irq_restore(flags);  	touch_softlockup_watchdog();+	clocksource_touch_watchdog(); }  static void tick_nohz_stop_idle(int cpu) ????{.n?+???????+%?????ݶ??w??{.n?+????{??G?????{ay?ʇڙ?,j??f???h?????????z_??(?階?ݢj"???m??????G????????????&???~???iO???z??v?^?m????????????I?