Re: [PATCH 3/3] block: reimplement FLUSH/FUA to support merge
From: Darrick J. Wong
Date: Wed Mar 23 2011 - 19:37:23 EST
On Tue, Jan 25, 2011 at 12:39:24PM +0100, Jens Axboe wrote:
> On 2011-01-25 11:21, 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.
> >>> 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.
> > Jens, what do you think? If you don't object, let's put this through
> > linux-next.
> I like the approach, I'll queue it up for 2.6.39.
Is this patch set still on the merge list for 2.6.39?
> Jens Axboe
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