[Xen-devel] Re: [PATCH] cpu idle ticks show twice in xen pvm guest

[DuanZhenzhong <zhenzhong.duan@xxxxxxxxxx>]

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@xxxxxxxxxx>
> > > Signed-off-by: Joe Jin <joe.jin@xxxxxxxxxx>
> > >       
> > 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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