linux-kernel - Re: Why is NCQ enabled by default by libata? (2.6.20)

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Message-ID: <Pine.LNX.4.64.0703270554320.31853@p34.internal.lan>
Date:	Tue, 27 Mar 2007 05:55:44 -0400 (EDT)
From:	Justin Piszcz <jpiszcz@...idpixels.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
cc:	linux-kernel@...r.kernel.org
Subject: Re: Why is NCQ enabled by default by libata? (2.6.20)

On Sat, 24 Mar 2007, Alan Cox wrote:

> On Sat, 24 Mar 2007 12:38:02 -0400 (EDT)
> Justin Piszcz <jpiszcz@...idpixels.com> wrote:
>
>> Without NCQ, performance is MUCH better on almost every operation, with
>> the exception of 2-3 items.
>
> It depends on the drive. Generally NCQ is better but some drive firmware
> isn't too bright and there are probably still cases where we get bad
> interactions in the kernel code that want tuning too
>

Checking the benchmarks on various hardware websites, anandtech, 
hothardware and others, they generally all come to the same conclusion if 
there is only 1 thread using I/O (single user system) then NCQ off is the 
best.  I see 30-50MB/s faster speeds with NCQ turned off on two different 
SW RAID5s.

Justin.
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