linux-kernel - Re: Decreasing stime running confuses top

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Date:	Thu, 04 Oct 2007 15:32:23 -0400
From:	Chuck Ebbert <cebbert@...hat.com>
To:	Luca Tettamanti <kronos.it@...il.com>
CC:	Frans Pop <elendil@...net.nl>, Willy Tarreau <w@....eu>,
	LKML <linux-kernel@...r.kernel.org>,
	Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>,
	"Alexander E. Patrakov" <patrakov@....usu.ru>
Subject: Re: Decreasing stime running confuses top

On 10/04/2007 03:19 PM, Luca Tettamanti wrote:
>>>>>> The latter seems to be utime ...decreasing. No wonder if
>>>>>> arithmetics will give strange results (probably top is using
>>>>>> unsigned delta?)...
>>>>> Hmm, minor miscounting from my side, stime seems more appropriate...
>>>> So, is it normal that stime decreases sometimes or a kernel bug?
>>>> /me expects the last...
>>> Let me guess... Dual core AMD64 ?
>> Nope: Intel(R) Pentium(R) D CPU 3.20GHz
> 
> I just notice the same thing here, with a Core2 Duo (which is supposed
> to have synced TSCs) and working HPET.
> 
>> The following may well be relevant.
>> With 2.6.22 and early 2.6.23-rc kernels (rc3-rc6) I often had this in my
>> kernel log (see http://lkml.org/lkml/2007/9/16/45):
>>    checking TSC synchronization [CPU#0 -> CPU#1]:
>>    Measured 248 cycles TSC warp between CPUs, turning off TSC clock.
>>    Marking TSC unstable due to check_tsc_sync_source failed
> 
> I don't see this though, TSCs are always syncronized between the 2
> cores.
> 

Is CONFIG_VIRT_CPU_ACCOUNTING set?

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