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Re: [Qemu-devel] [BUG] Regression of exec migration

From: Anthony Liguori
Subject: Re: [Qemu-devel] [BUG] Regression of exec migration
Date: Thu, 27 Aug 2009 09:13:42 -0500
User-agent: Thunderbird (X11/20090320)

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.


Anthony Liguori

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