On Tue, Jan 25, 2011 at 11:21:28AM +0100, Tejun Heo wrote: > Hello, Darrick. > > On Mon, Jan 24, 2011 at 12:31:55PM -0800, Darrick J. Wong wrote: > > > So, I think it's better to start with something simple and improve it > > > with actual testing. If the current simple implementation can match > > > Darrick's previous numbers, let's first settle the mechanisms. We can > > > > Yep, the fsync-happy numbers more or less match... at least for 2.6.37: > > http://tinyurl.com/4q2xeao > > Good to hear. Thanks for the detailed testing. > > > I'll give 2.6.38-rc2 a try later, though -rc1 didn't boot for me, so these > > numbers are based on a backport to .37. :( > > Well, there hasn' been any change in the area during the merge window > anyway, so I think testing on 2.6.37 should be fine. Well, I gave it a spin on -rc2 with no problems and no significant change in performance, so: Acked-by: Darrick J. Wong <djwong@xxxxxxxxxx> > > > I don't really think we should design the whole thing around broken > > > devices which incorrectly report writeback cache when it need not. > > > The correct place to work around that is during device identification > > > not in the flush logic. > > > > elm3a4_sas and elm3c71_extsas advertise writeback cache yet the > > flush completion times are suspiciously low. I suppose it could be > > useful to disable flushes to squeeze out that last bit of > > performance, though I don't know how one goes about querying the > > disk array to learn if there's a battery behind the cache. I guess > > the current mechanism (admin knob that picks a safe default) is good > > enough. > > Yeap, that or a blacklist of devices which lie. Hmm... I don't think a blacklist would work for our arrays, since one can force them to run with write cache and no battery. I _do_ have a patch that adds a sysfs knob to the block layer to drop flush/fua if the admin really really really wants it, so I'll send that out shortly along with another one to remove the barrier= mount option from ext4. (Unless the screams of objection rain from the skies. :)) --D -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
