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Date: Wed, 01 Dec 2010 10:49:32 -0600
From: Anthony Liguori <anthony@codemonkey.ws>
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Subject: [Qemu-devel] Re: [PATCH 10/10] Maintaing number of dirty pages
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To: Avi Kivity <avi@redhat.com>
Cc: qemu-devel@nongnu.org, Juan Quintela <quintela@redhat.com>

On 12/01/2010 10:43 AM, Avi Kivity wrote:
> On 12/01/2010 06:33 PM, Anthony Liguori wrote:
>>>> BTW, by this logic, even a 1-byte dirty bitmap is only 16mb which can
>>>> be read in less than 16ms so where is the reported 24 minute stall
>>>> coming from?
>>> a) we read the bitmap more than once
>>
>> Not in a single iteration which is what the "stall" would consist of.
>>
>>> b) the 1ms is based on "we read" it with longs and optimized, just now
>>>     we have to read it by byte and inside the byte.
>>
>> Byte accesses verse long access doesn't turn 16ms into 24 minutes.
>
> We need actual measurements instead of speculations.

Yes, I agree 100%.  I think the place to start is what I suggested in a 
previous note in this thread, we need to measure actual stall time in 
the guest.

Regards,

Anthony Liguori