bad NFS/UDP performance
rwatson at FreeBSD.org
Mon Sep 29 12:22:34 UTC 2008
On Mon, 29 Sep 2008, Oliver Fromme wrote:
> Danny Braniss wrote:
> > Grr, there goes binary search theory out of the window,
> > So far I have managed to pinpoint the day that the changes affect the
> > throughput:
> > 18/08/08 00:00:00 19/08/08 00:00:00
> > (I assume cvs's date is GMT).
> > now would be a good time for some help, specially how to undo changes, my
> > knowledge of csup/cvs are close to zero.
> So you've nailed to down to this 24-hour window:
> I'm afraid that r181822 by rwatson is the most likely candidate that might
> be causing the regression.
If we can confirm that it was that specific change, then I can create a patch
to restore exclusive locking for UDP and we can see if it was the general move
to rwlocking, or specifically the read-locking of certain data structures.
Perhaps what we've done is moved contention from a mutex to a sleep lock,
reducing the efficiency of handling contention? Adding Kris to the CC line
because he often has useful insights on this sort of thing.
Robert N M Watson
University of Cambridge
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