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Re: [Xen-devel] time accounting problem in pvops kernel

To: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Subject: Re: [Xen-devel] time accounting problem in pvops kernel
From: Jed Smith <jed@xxxxxxxxxx>
Date: Wed, 18 Aug 2010 10:17:33 -0400
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On Aug 18, 2010, at 3:49 AM, Paolo Bonzini wrote:

> On 08/18/2010 12:51 AM, Jeremy Fitzhardinge wrote:
>>  On 08/17/2010 10:29 AM, Paolo Bonzini wrote:
>>> Hi,
>>> while experimenting a bit with time.c we found a bug in time
>>> accounting.  Basically, /proc/stat counts idle time twice for PV guests
>>> running a pvops kernel
>> What version?
> I was using the latest RHEL6 snapshot + the 16-patch blkfront series (i.e. 
> without the patch you pointed out).
>> Upstream and stable kernels contain the changeset "xen:
>> drop xen_sched_clock in favour of using plain wallclock time" which
>> should fix a lot of timekeeping/scheduling problems.
> I'll try this patch; however, offhand I don't see how it fixes the problem of 
> calling account_idle_ticks twice.

I saw this too, even with said patch applied.  To avoid this being simply a
'me too!' message, I noticed that it aggravated Munin quite a bit.  The CPU
plugin detects 800% of idle on a 4-core machine, but only idle time is off.


Jed Smith
Systems Administrator
Linode, LLC
+1 (609) 593-7103 x1209

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