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[Qemu-devel] Relative/Absolute timing snapshot problem

From: Clemens Kolbitsch
Subject: [Qemu-devel] Relative/Absolute timing snapshot problem
Date: Fri, 18 Mar 2011 13:39:33 -0700
User-agent: KMail/1.13.5 (Linux/2.6.35-28-generic; KDE/4.5.1; x86_64; ; )

Hi list,

strange situation: When I create a snapshot using Qemu 0.14.0 stable, 
everything works smoothly and resuming the CPU takes about 1-2 seconds. If I 
don't use the snapshot file for some time, the time it takes to resume grows 
by 2-3 seconds per day. At the moment, I'm looking at a snapshot file from 
last week and it takes nearly 30 seconds to load.

Funny thing about it: if I turn my system time back to the date when the 
snapshot was created (or before that), resuming CPU works within the expected 
1-2 seconds. I have _very briefly_ looked into it and it seems like Qemu 
spends an aweful long amount of time catching up with timer execution -- is it 
possible that these are stored using absolute time instead of relative timing?

I am using qcow2 file format, because I absolutely rely on CPU-snapshots and 
support for base-files. I have read here and there that it is more or less 
broken (or at least very slow), but with the correct cache-options it works 
for me (except for this bug, of course).

Has anyone encountered this or should I start looking into it (although I have 
some experience with the core source, I'm not very experienced with the 
snapshotting code).


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