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Re: [Xen-devel] A clocksource question

To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Subject: Re: [Xen-devel] A clocksource question
From: Joanna Rutkowska <joanna@xxxxxxxxxxxxxxxxxxxxxx>
Date: Fri, 12 Mar 2010 01:38:01 +0100
Cc: Ian Pratt <Ian.Pratt@xxxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
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On 03/12/2010 01:49 AM, Jeremy Fitzhardinge wrote:
> On 03/11/2010 04:27 PM, Joanna Rutkowska wrote:
>> I think that the important clue is this message appearing in my dmesg
>> (in Dom0 and also in DomUs):
>> hrtimer: interrupt too slow, forcing clock min delta to 540150561 ns
>> This is almost 0.5s (!) and I think this might explain my kbd hiccup. I
>> wrote that I feel it every 10s or so, but when I was playing on my
>> system without jiffies setting today, I saw this hiccup occurring much
>> more often; in fact it was more of a "slow keyboard/system" feeling than
>> a hiccup".
> Yes, its definitely a good clue.  It could point to a Xen scheduler
> issue (I assume you don't have any other busy domains when this is going
> on), but that wouldn't explain why it works OK with jiffies.  Perhaps
> there's a problem with programming the timer so that sometimes it gets
> missed and the system doesn't get a kick until some subsequent event
> (whereas with clocksource=jiffies there'll always be a timer in the next
> 100ms).
One detail: when I boot the system and there is only Dom0 running,
everything seems ok. Only after I start at least one VM the problem
becomes noticeable. But the other VM(s) is pretty much idle (as xentop

When I kill all the other VMs, so that Dom0 is alone again, the problem
does *not* seem to go away, strangely...


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