Re: Odd IDE performance drop 2.4 vs 2.6?

[Jens Axboe]

On Mon, Jun 13 2005, Alan Cox wrote:
> On Llu, 2005-06-13 at 15:06, Nick Piggin wrote:
> > > Make sure you have pre-empt disabled and the antcipatory I/O scheduler
> > > disabled. 
> > > 
> > I don't think that those could explain it.
> 
> Try it and see. The anticipatory I/O scheduler does horrible things to
> my IDE streaming performance numbers and to swap performance. It tries
> to merge I/O by delaying it which is deeply ungood when it comes to IDE
> streaming even if its good for general I/O.

Well, AS should only intentionally delay when it has competing threads
fighting for the disk. For a single threaded io case like hdparm, it
should never idle the drive. It never delays to increase merge rate, or
anything like that - only to increase spatial locality on the drive for
two or more processes accessing it simultanously.

-- 
Jens Axboe

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