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Re: [Qemu-devel] [RESEND][PATCH 0/3] Fix guest time drift under heavy lo
From: |
Gleb Natapov |
Subject: |
Re: [Qemu-devel] [RESEND][PATCH 0/3] Fix guest time drift under heavy load. |
Date: |
Mon, 10 Nov 2008 16:37:50 +0200 |
On Sun, Nov 09, 2008 at 10:36:59AM -0600, Anthony Liguori wrote:
> Gleb Natapov wrote:
>> On Thu, Nov 06, 2008 at 09:37:56AM -0600, Anthony Liguori wrote:
>>
>>
>> Yes indeed. With raw image copy benchmark no longer runs enough time to
>> produce time drift big enough to be visible. So I ran this disk test
>> utility http://69.90.47.6/mybootdisks.com/mybootdisks_com/nu2/bst514.zip
>> for ~12 hours and the time drift was 12 secs (if I weren't so lazy and
>> wrote bat file to copy c:\windows in a loop I am sure result would be the
>> same). This is on completely idle host.
>>
>
> What frequency is the guest running at? If it's running at 100hz, then
Windows program RTC to 64hz frequency.
> it missed a tick once every 36 seconds. This means that the guest
> couldn't run long enough to handle a timer interrupt (which should be a
> relatively small number of cycles) in a 10ms period.
>
10ms is for qemu + guest, not just guest.
> Does this drift go away with the TDF patches? This almost makes me
> think that we aren't delivering interrupts at the right frequency and
> we're simply accumulating error. In theory, the TDF patches shouldn't
> help that.
I haven't checked TDF patch yet, but I inserted prints into RTC
emulation to check it interrupt are really missed and they are. And
after 64 lost interrupts (took slightly more then one hour) the time
drift was 1 second, so TDF patches should fix that.
>
> Otherwise, I'm curious if you have any insight into where we're pausing
> for 10ms that's causing the missed interrupt?
>
Don't know yet.
> We could also be missing ticks somehow. I think this warrants further
> investigation.
>
This is not the case from what I observe.
--
Gleb.
- Re: [Qemu-devel] [RESEND][PATCH 0/3] Fix guest time drift under heavy load., (continued)
- Re: [Qemu-devel] [RESEND][PATCH 0/3] Fix guest time drift under heavy load., Paul Brook, 2008/11/06
- Re: [Qemu-devel] [RESEND][PATCH 0/3] Fix guest time drift under heavy load., Anthony Liguori, 2008/11/06
- Re: [Qemu-devel] [RESEND][PATCH 0/3] Fix guest time drift under heavy load., Gleb Natapov, 2008/11/06
- Re: [Qemu-devel] [RESEND][PATCH 0/3] Fix guest time drift under heavy load., Anthony Liguori, 2008/11/06
- Re: [Qemu-devel] [RESEND][PATCH 0/3] Fix guest time drift under heavy load., Gleb Natapov, 2008/11/08
- Re: [Qemu-devel] [RESEND][PATCH 0/3] Fix guest time drift under heavy load., Dor Laor, 2008/11/08
- Re: [Qemu-devel] [RESEND][PATCH 0/3] Fix guest time drift under heavy load., Gleb Natapov, 2008/11/09
- Re: [Qemu-devel] [RESEND][PATCH 0/3] Fix guest time drift under heavy load., Anthony Liguori, 2008/11/09
- Re: [Qemu-devel] [RESEND][PATCH 0/3] Fix guest time drift under heavy load., Avi Kivity, 2008/11/09
- Re: [Qemu-devel] [RESEND][PATCH 0/3] Fix guest time drift under heavy load., Anthony Liguori, 2008/11/09
- Re: [Qemu-devel] [RESEND][PATCH 0/3] Fix guest time drift under heavy load.,
Gleb Natapov <=
- Re: [Qemu-devel] [RESEND][PATCH 0/3] Fix guest time drift under heavy load., Anthony Liguori, 2008/11/10
- Re: [Qemu-devel] [RESEND][PATCH 0/3] Fix guest time drift under heavy load., Gleb Natapov, 2008/11/10
- Re: [Qemu-devel] [RESEND][PATCH 0/3] Fix guest time drift under heavy load., Anthony Liguori, 2008/11/10
- Re: [Qemu-devel] [RESEND][PATCH 0/3] Fix guest time drift under heavy load., Gleb Natapov, 2008/11/10
- Re: [Qemu-devel] [RESEND][PATCH 0/3] Fix guest time drift under heavy load., Gleb Natapov, 2008/11/11
- Re: [Qemu-devel] [RESEND][PATCH 0/3] Fix guest time drift under heavy load., Anthony Liguori, 2008/11/11
- Re: [Qemu-devel] [RESEND][PATCH 0/3] Fix guest time drift under heavy load., Anthony Liguori, 2008/11/11
- Re: [Qemu-devel] [RESEND][PATCH 0/3] Fix guest time drift under heavy load., Gleb Natapov, 2008/11/12
- Re: [Qemu-devel] [RESEND][PATCH 0/3] Fix guest time drift under heavy load., Glauber Costa, 2008/11/12
- Re: [Qemu-devel] [RESEND][PATCH 0/3] Fix guest time drift under heavy load., Dor Laor, 2008/11/12