linux-kernel - Re: [PATCH] cpu idle ticks show twice in xen pvm guest

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Date:	Tue, 11 Oct 2011 11:16:42 +0800
From:	DuanZhenzhong <zhenzhong.duan@...cle.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	linux-x86_64@...r.kernel.org, linux-kernel@...r.kernel.org,
	xen-devel@...ts.xensource.com, Joe Jin <joe.jin@...cle.com>
Subject: Re: [PATCH] cpu idle ticks show twice in xen pvm guest

Jeremy Fitzhardinge wrote:
> On 10/10/2011 08:53 AM, Konrad Rzeszutek Wilk wrote:
>   
>> On Wed, Oct 05, 2011 at 10:11:58PM -0700, Zhenzhong Duan wrote:
>>     
>>> Run below test on xen pvm.
>>> # x=$(cat /proc/stat | grep cpu0 | awk '{print $5}') && sleep 60  \
>>> && y=$(cat /proc/stat | grep cpu0 | awk '{print $5}') \
>>> && echo -e  "X:$x\nY:$y\nIDLE:" $(echo "scale=3; ($y-$x)/6000*100" | bc)
>>>
>>> @ X:58562301
>>> @ Y:58574282
>>> @ IDLE: 199.600
>>>
>>> Normal idle percent should be around 100%.
>>> xen_timer_interrupt called account_idle_ticks to account hypervisor stolen idle ticks 
>>> but these ticks will be accounted again when idle ticks restarted.
>>>
>>> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@...cle.com>
>>> Signed-off-by: Joe Jin <joe.jin@...cle.com>
>>>       
>> Please in the future also CC the maintainers (you can get that using
>> the scripts/get_maintainer.pl).
>>
>> Jeremy, any thoughts?
>>     
>
> Does this affect the accounting of stolen ticks?  If it does, that's not
> necessarily a showstopper for this patch, but we'll need to do some more
> thinking about it.  Certainly, accurate accounting for idleness is
> important.
>
>     J
>
>   
Thanks Konrad for point out that.
In Original kernel, tick_nohz_restart_sched_tick and 
do_stolen_accounting both called account_idle_ticks.
For a idle pvm, idle/iowait maybe doubled apparently.
Normally Y-X should get close to 6000 in idle system, but in my test 
it's 11981.
But I am still not sure if patch has any impact to other part. Thanks
>>> diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
>>> index 163b467..5dcbc91 100644
>>> --- a/arch/x86/xen/time.c
>>> +++ b/arch/x86/xen/time.c
>>> @@ -151,7 +151,6 @@ static void do_stolen_accounting(void)
>>>  
>>>  	ticks = iter_div_u64_rem(blocked, NS_PER_TICK, &blocked);
>>>  	__this_cpu_write(xen_residual_blocked, blocked);
>>> -	account_idle_ticks(ticks);
>>>  }
>>>  
>>>  /* Get the TSC speed from Xen */
>>> --
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>>>       
>
>   


-- 
Regards
zhenzhong
--
Oracle Building, No.24 Building, Zhongguancun Software Park
Haidian District, Beijing 100193, China

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