linux-kernel - Re: [PATCH 0/3] Convert libata pio task to slow-work

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Message-ID: <4A96830F.9040805@kernel.org>
Date:	Thu, 27 Aug 2009 21:58:55 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Jens Axboe <jens.axboe@...cle.com>
CC:	linux-kernel@...r.kernel.org, linux-ide@...r.kernel.org,
	alan@...rguk.ukuu.org.uk, jeff@...zik.org, dhowells@...hat.com
Subject: Re: [PATCH 0/3] Convert libata pio task to slow-work

Hello, Jens.

Jens Axboe wrote:
>> It would be nice if merging of this series and the lazy work can be
>> held a bit but there's no harm in merging either.  If the concurrency
>> managed workqueue turns out to be a good idea, we can replace it then.
> 
> It can wait, what you describe above sounds really cool and would
> hopefully allow us to get rid of all workqueues (provided it scales well
> and doesn't fall down on cache line contention with many different
> instances pounding on it).

Almost all operations are per-cpu so cache lines shouldn't bounce too
much.  The only part I worry about is the part which checks whether a
work is currently executing on the current cpu which currently is
implemeted as a hash table.  The hash table is only 16 pointers long
and will be mostly empty so hopefully it doesn't add any significant
overhead.

> Care to post it? I know you don't think it's perfect yet, but it would
> make a lot more sense to throw effort into this rather than waste time
> on partial solutions.

I have this printed out code with full of red markings from proof
reading and flush implementation is mostly broken.  Please give me a
couple of days.  I'll post a rough unsplit version which at least
compiles with the planned changes applied by the end of the week.  :-)

Thanks.

-- 
tejun
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