[dm-devel] dm-kcopyd: Delayed unplug of the queues
Mike Snitzer
snitzer at redhat.com
Fri Nov 19 22:18:31 UTC 2010
On Sun, Oct 24 2010 at 9:03pm -0400,
Mikulas Patocka <mpatocka at redhat.com> wrote:
> dm-kcopyd: Delayed unplug of the queues
>
> This patch improves performance aby about 20% when writing to the snapshot
> origin. We keep track of two block devices to unplug (one for read and the
> other for write) and unplug them when exiting "do_work" thread. If there are
> more devices used (in theory it could happen, in practice it is rare), we
> unplug immediatelly.
Again, more specifics on how you realized this 20% performance would be
appreciated. I'd imagine this patch is really where the increased
latency comes back (due to removing immediate unplug)?
But does the fact that >2 devices will unplug immediately mitigate the
worst of the higher latency (e.g. for DM mirrors with >2 legs)?
Mike
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