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From: | Avi Kivity |
Subject: | Re: [Qemu-devel] Re: [RFC][STABLE 0.13] Revert "qcow2: Use bdrv_(p)write_sync for metadata writes" |
Date: | Tue, 24 Aug 2010 15:39:13 +0300 |
User-agent: | Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.7) Gecko/20100720 Fedora/3.1.1-1.fc13 Lightning/1.0b2pre Thunderbird/3.1.1 |
On 08/24/2010 03:35 PM, Kevin Wolf wrote:
I don't know how bad the performance regression is, and how large the integrity risk is. I'd default towards preserving integrity, but maybe this situation is different.I have reports of installations taking like 50 min instead of 14 min. My own qemu-io based test goes up from 1 s to 23 s. And I think the winner is Michael's image conversion which went up from 30 s to 49 min. So it's not like we're talking about just some 10 or 20 percent.
Image conversion should be done with cache=unsafe (with an fsync at the end to make sure a guest isn't launched with volatile data in the cache[1]). The io test isn't a user workload.
The 14 min -> 50 min regression is pretty bad, but I'm not sure it's bad enough to merit risking user data.
[1] or better, when launching a guest with cache!=unsafe start with an fsync to make sure it's on disk.
-- error compiling committee.c: too many arguments to function
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