linux-kernel - Re: Fwd: [PATCH 0/5] cfq-iosched: improve latency for no-idle queues (v3)

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Message-ID: <20091103201802.GL8742@kernel.dk>
Date:	Tue, 3 Nov 2009 21:18:02 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Corrado Zoccolo <czoccolo@...il.com>
Cc:	Linux-Kernel <linux-kernel@...r.kernel.org>,
	Jeff Moyer <jmoyer@...hat.com>
Subject: Re: Fwd: [PATCH 0/5] cfq-iosched: improve latency for no-idle
	queues (v3)

On Tue, Nov 03 2009, Corrado Zoccolo wrote:
> Hi Jens,
> Jeff did some testing of this patchset on his NCQ-enabled SSD (the
> 30GB OCZ Vertex).
> The test suite contained various multiple competing workloads
> scenarios, and was run on for-2.6.33 and cfq-2.6.33 branches.
> 
> Max latencies were reduced in most cases, and we had also improvements
> on bandwidth side in some scenarios, especially
> for multiple random readers, either alone or competing with writes.
> 2 random readers aggregate bw increased from 48356 to 74205
> and 4 random readers vs 1 seq writer:
> * aggregate reader bw increased from 35242 to 56400
> * writer bandwidth increased from 33269 to 55127
> * maximum latency on read decreased from 535 to 324
> * maximum latency on writes decreased from 22243 to 1153
> It's a win on all measures.
> The effect increasing the number of readers to 32 (latency_test_2.fio)
> is even more visible (max read latency reduced from 3305 to 268,
> aggregated read BW increased from 32894 to 164571).
> 
> The only case where I see an increased max latency is for 2 random
> readers vs 1 seq reader:
> 
> for-2.6.33:
> randomread.0: read_bw = 15,418K
> randomread.1: read_bw = 15,399K
> seqread: read_bw = 409K
> 0: read_bw = 31226
> 0: read_lat_max = 11.589
> 0: read_lat_avg = 3.22366666666667
> 
> cfq-2.6.33:
> randomread.0: read_bw = 10,065K
> randomread.1: read_bw = 10,067K
> seqread: read_bw = 101M
> 0: read_bw = 121132
> 0: read_lat_max = 303
> 0: read_lat_avg = 0.282333333333333
> 
> but here the increased latency is paid back by a large increase in
> sequential read BW (the max latency is, btw, experienced by the seq
> reader, so I think it is a fair behaviour).
> 
> Jeff observed that the for-2.6.33 numbers were worse than his baseline
> runs, probably due to changed hw_tag detection.
> My patchset is much less sensible to hw_tag on SSDs (since there are
> much less situations in which it would idle), so my numbers are
> unaffected.

Thanks a lot for your testing. My testing on cfq-2.6.33 looks good too,
so I pulled it into for-2.6.33 today.

Since for-linus contains conflicting changes, can you and Jeff please
double check that everything is still in order? The interesting bit here
is the merge with for-2.6.33 and the coop limit from Shaohua Li. I did
the straight forward merge, but we likely just need to drop that logic
since the coop concept is radically different given that we merge and
break queues in for-2.6.33.

-- 
Jens Axboe

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