Re: [GIT PULL] Ext3 latency fixes

Arjan van de Ven
2009-04-05T18:55:08Z

On Sun, 5 Apr 2009 10:01:06 -0700 (PDT)
Linus Torvalds <torvalds@linux-foundation.org> wrote:
> Also, one of the issues seems to literally be that the higher-level
> request handling doesn't care AT ALL about the priority. Allocating
> the request itself does keep reads and writes separated, but if the
> request is a SYNCIO request, and non-sync writes have filled up th
> write requests, we'll have to wait for the background writes to free
> up requests.
>
> That is quite possibly the longest wait we have in the system.

it often is; latencytop tends to point that out.
>
> See get_request():

our default number of requests is so low that we very regularly hit the
limit. In addition to setting kjournald to higher priority, I tend to
set the number of requests to 4096 or so to improve interactive
performance on my own systems. That way at least the elevator has a
chance to see the requests ;-)

--
Arjan van de Ven Intel Open Source Technology Centre
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