From: Andi Kleen <andi@firstfloor.org>
To: Jens Axboe <axboe@kernel.dk>
Cc: "Alan D. Brunelle" <Alan.Brunelle@hp.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Jens Axboe <jens.axboe@oracle.com>
Subject: Re: [RFC][PATCH 0/3] Skip I/O merges when disabled
Date: Thu, 24 Apr 2008 16:15:54 +0200 [thread overview]
Message-ID: <4810961A.4000104@firstfloor.org> (raw)
In-Reply-To: <67E36C56-E149-4C87-8788-05BA43C1C2AD@kernel.dk>
> Not a good idea IMHO, it's much better with an explicit setting. That
> way you don't introduce indeterministic behavior.
So you would be deterministically slower.
Another way to avoid this problem would be to keep the statistics per
IO context, then the same run of a program would always get the same
behaviour. Drawback is that if your non mergeable workload consists of
lots of short running processes (like a shell script) the optimization
wouldn't work. Not sure if it's really practical, but it would be an option.
I think in modern systems with caches etc. you typically have enough
non quite deterministic and other surprising and hard to analyze
behaviour anyways, so a little more doesn't make much difference.
-Andi
next prev parent reply other threads:[~2008-04-24 14:16 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-04-23 19:08 [RFC][PATCH 0/3] Skip I/O merges when disabled Alan D. Brunelle
2008-04-23 19:12 ` [RFC][PATCH 1/3] Add flag and sysfs interfaces Alan D. Brunelle
2008-04-23 19:14 ` [RFC][PATCH 2/3] Have __make_request skip merges when disabled Alan D. Brunelle
2008-04-23 19:15 ` [RFC][PATCH 3/3] Do not use rqhash when merges disabled Alan D. Brunelle
2008-04-24 0:37 ` Aaron Carroll
2008-04-24 0:59 ` Alan D. Brunelle
2008-04-24 2:07 ` Aaron Carroll
2008-04-24 7:09 ` [RFC][PATCH 0/3] Skip I/O merges when disabled Jens Axboe
2008-04-24 12:09 ` Alan D. Brunelle
2008-04-25 8:38 ` Jens Axboe
2008-04-25 11:17 ` Alan D. Brunelle
2008-04-25 11:25 ` Jens Axboe
2008-04-25 12:06 ` Aaron Carroll
2008-04-25 12:14 ` Jens Axboe
2008-04-25 12:17 ` Alan D. Brunelle
2008-04-28 16:36 ` Alan D. Brunelle
2008-04-29 7:37 ` Jens Axboe
2008-04-24 20:38 ` Alan D. Brunelle
2008-04-24 13:29 ` Andi Kleen
2008-04-24 13:59 ` Jens Axboe
2008-04-24 14:13 ` Alan D. Brunelle
2008-04-24 15:05 ` Jens Axboe
2008-04-24 22:04 ` Carl Henrik Lunde
2008-04-25 7:13 ` Andi Kleen
2008-04-24 14:15 ` Andi Kleen [this message]
2008-04-24 15:04 ` Jens Axboe
2008-04-24 15:53 ` David Collier-Brown
2008-04-24 16:29 ` Alan D. Brunelle
2008-04-24 13:31 ` Alan D. Brunelle
2008-04-24 13:43 ` Alan D. Brunelle
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