linux-kernel - Re: 2.6.21.1 - 97% wait time on IDE operations

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Date:	Sat, 26 May 2007 08:13:06 -0700
From:	"Ray Lee" <ray-lk@...rabbit.org>
To:	"Tommy Vercetti" <vercetti@...w.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: 2.6.21.1 - 97% wait time on IDE operations

On 5/26/07, Tommy Vercetti <vercetti@...w.org> wrote:
> I was trying to get answer to my question around, but no one knows.
> I do have DMA turned on, etc, yet - on extensive harddrive operations wait

You may have DMA turned on, but it may be ineffectual if you don't
have the right IDE driver handing your disk.

> time is 90+% , which means that machine is waiting, rather than doing
> something meanwhile. (I guess).

What does hdparm -tT /dev/hda say? If the numbers are reasonable
(~400MB/s for cache reads, ~25MB/s for buffered disk reads), then
you're just doing a lot of seeking on the drive, and that takes a long
time. (Drives can seek about 100 times a second. If every seek reads
only 4k of data, that's 400k of data processed per second, or a lot of
time spent with the CPU waiting on I/O.)
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