From: Jeff Garzik <jeff@garzik.org>
To: Justin Piszcz <jpiszcz@lucidpixels.com>
Cc: linux-kernel@vger.kernel.org,
IDE/ATA development list <linux-ide@vger.kernel.org>
Subject: Re: Why is NCQ enabled by default by libata? (2.6.20)
Date: Tue, 27 Mar 2007 01:59:21 -0400 [thread overview]
Message-ID: <4608B2B9.7090503@garzik.org> (raw)
In-Reply-To: <Pine.LNX.4.64.0703241232580.11608@p34.internal.lan>
Justin Piszcz wrote:
> Without NCQ, performance is MUCH better on almost every operation, with
> the exception of 2-3 items.
Variables to take into account:
* the drive (NCQ performance wildly varies)
* the IO scheduler
* the filesystem (if not measuring direct to blkdev)
* application workload (or in your case, benchmark tool)
* in particular, the threaded-ness of the apps
For the overwhelming majority of combinations, NCQ should not /hurt/
performance.
For the majority of combinations, NCQ helps (though it may not be often
that you use more than 4-8 tags).
In some cases, NCQ firmware may be broken. There is a Maxtor firmware
id, and some Hitachi ids that people are leaning towards recommending be
added to the libata 'horkage' list.
Jeff
next parent reply other threads:[~2007-03-27 5:59 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <Pine.LNX.4.64.0703241232580.11608@p34.internal.lan>
2007-03-27 5:59 ` Jeff Garzik [this message]
2007-03-27 14:26 ` Why is NCQ enabled by default by libata? (2.6.20) Mark Lord
2007-03-27 18:18 ` Mark Rustad
2007-03-27 18:38 ` Jeff Garzik
2007-03-27 22:12 ` Mark Rustad
2007-03-31 12:55 ` Ric Wheeler
2007-03-27 16:16 linux
2007-03-27 16:25 ` Justin Piszcz
2007-03-27 16:41 ` linux
2007-03-27 16:44 ` Justin Piszcz
2007-03-27 16:58 ` linux
2007-03-27 17:03 ` Justin Piszcz
2007-03-28 14:42 ` Phillip Susi
2007-03-28 14:48 ` Jeff Garzik
2007-03-28 15:22 ` Andy Warner
2007-03-29 17:28 ` Phillip Susi
2007-03-29 18:40 ` linux
2007-03-29 18:51 ` Jeff Garzik
2007-03-29 21:35 ` Alan Cox
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