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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