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Re: pagebuf_prepare_write doesn't kmap the page

To: Steve Lord <lord@xxxxxxx>
Subject: Re: pagebuf_prepare_write doesn't kmap the page
From: Jens Axboe <axboe@xxxxxxx>
Date: Wed, 31 Jan 2001 18:29:49 +0100
Cc: Marcelo Tosatti <marcelo@xxxxxxxxxxxxxxxx>, David Wragg <dpw@xxxxxxxxxxxx>, linux-xfs@xxxxxxxxxxx
In-reply-to: <200101311637.f0VGb5n26720@xxxxxxxxxxxxxxxxxxxx>; from lord@xxxxxxx on Wed, Jan 31, 2001 at 10:37:05AM -0600
References: <marcelo@xxxxxxxxxxxxxxxx> <200101311637.f0VGb5n26720@xxxxxxxxxxxxxxxxxxxx>
Sender: owner-linux-xfs@xxxxxxxxxxx
On Wed, Jan 31 2001, Steve Lord wrote:
> It is difficult to nail down the cause yet, but dbench has taken a
> significant hit (40%). Single file (bonnie) is comparable with 2.4.0, the
> dbench issue may be related to the throttling being placed on the
> ll_rw_block interface by Jens' changes. The problem with working out
> a bottleneck in dbench is it is such a random pile of stuff that
> you really cannot point a finger at any one thing. I need to go
> find some more deterministic measurements.
> The performance drop off is not limited to xfs though ext2 appears
> to suffer as well.

You can easily disable the throttling of locked buffers by just
defining blk_started_io and blk_finished_io to do nothing. What
disk are you using, and how much RAM in the machine?

Also, is dbench the only bench affected?

Jens Axboe

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