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Date: Thu, 27 Aug 2009 09:13:42 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
MIME-Version: 1.0
Subject: Re: [Qemu-devel] [BUG] Regression of exec migration
References: <E341C6E8-D4BC-4964-A527-AE1CD22F4D54@irisa.fr>
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To: Pierre Riteau <Pierre.Riteau@irisa.fr>
Cc: Chris Lalancette <clalance@redhat.com>, qemu-devel@nongnu.org

Pierre Riteau wrote:
> [Sorry Chris, resending without the giant attachments.]
>
> Commit 907500095851230a480b14bc852c4e49d32cb16d makes exec migration 
> much slower than before.
> I'm running the latest HEAD of qemu, on Debian Lenny 5.0.2.
>
> I'm migrating a fully booted Linux VM (also running Lenny) with 128MB 
> of RAM to a file, using the following command: migrate "exec: cat > 
> vmimage". The resulting file has a size of 57MB (because we save only 
> what is allocated from the 128MB).
> With the current HEAD, it takes from 15 to 40 seconds (it's variable) 
> to perform the migration to the file.
> With commit 907500095851230a480b14bc852c4e49d32cb16d reverted (or just 
> commenting the "socket_set_nonblock(s->fd);" statement), it takes 
> about 3 seconds.

Without that changeset, it wasn't a live migration.  The better way to 
compare would be to issue stop before doing the migrate and compare that 
time with the previous time.

When a migration is live, it's iterative which means there's more work 
to do.

> only be retried after 100 ms (the next timer tick?).

We should be selecting on the fd so it will wait until we can write to it.

Regards,

Anthony Liguori