[Lustre-devel] COS performance issues

[Andreas Dilger]

On Oct 08, 2008  15:44 +0400, Alexander Zarochentsev wrote:
> I think the problem is that COS defers processing of replies to
> transaction commit time.  When commit happens, MDS has to process
> thousands of replies (about 14k replies per commit in the test 3.a)
> in short period of time. I guess the mdt service threads all woken
> up and spin trying to get the service svr_lock. Processing of new
> requests may also suffer of this.

Can you please explain what replies are being blocked?  It can't be the
create replies or the clients would be blocked waiting after starting a
single create each.

I think the thread and lock contention is only part of the issue - if all
of these replies are blocked until transaction commit this wastes all of
the bandwidth on the network while the replies are being held.

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.