On 11/30/2010 01:15 AM, Paolo Bonzini wrote:
On 11/30/2010 03:11 AM, Anthony Liguori wrote:
BufferedFile should hit the qemu_file_rate_limit check when the socket
buffer gets filled up.
The problem is that the file rate limit is not hit because work is
done elsewhere. The rate can limit the bandwidth used and makes QEMU
aware that socket operations may block (because that's what the
buffered file freeze/unfreeze logic does); but it cannot be used to
limit the _time_ spent in the migration code.
Yes, it can, if you set the rate limit sufficiently low.
The caveats are 1) the kvm.ko interface for dirty bits doesn't scale for
large memory guests so we spend a lot more CPU time walking it than we
should 2) zero pages cause us to burn a lot more CPU time than we
otherwise would because compressing them is so effective.
In the short term, fixing (2) by accounting zero pages as full sized
pages should "fix" the problem.
In the long term, we need a new dirty bit interface from kvm.ko that
uses a multi-level table. That should dramatically improve scan
performance. We also need to implement live migration in a separate
thread that doesn't carry qemu_mutex while it runs.
Regards,
Anthony Liguori
Paolo
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
