Re: [PATCH] as-iosched: update alias handling

[Nick Piggin <nickpiggin@yahoo.com.au>]

Jens Axboe wrote:
> On Thu, Nov 10 2005, Tejun Heo wrote:
>
> > Unlike other ioscheds, as-iosched handles alias by chaing them using
> > rq->queuelist.  As aliased requests are very rare in the first place,
> > this complicates merge/dispatch handling without meaningful
> > performance improvement.  This patch updates as-iosched to dump
> > aliased requests into dispatch queue as other ioscheds do.
> >
> > Signed-off-by: Tejun Heo <htejun@gmail.com>
>
>
> In theory the way 'as' handles the aliases is faster since we postpone
> pushing them to the dispatch list at the same point (and they have
> strong (if not identical) locality). But it is much simpler to just
> shove the offending requests onto the dispatch list.
>
> It's really up to Nick - what do you think? Leaving patch below.

I thought this was pretty cool, but in reality it could be that the
cost / benefit actually goes the wrong way due to added complexity
and rarity of alised requests.

Hmm... I can't bear to ack it ;) I'll close my eyes and let Jens
make the call!

> > ---
> >
> > Jens, I've tested this change for several hours, but it might be
> > better to postpone this change to next release.  It's your call.

It could go into mm now, but probably leave it for 2.6.16 unless
you have some other reason to really need it.

Nick

--
SUSE Labs, Novell Inc.

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