linux-kernel - Re: [PATCH 34/35] async: use workqueue for worker pool

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Message-ID: <4C2A3E4D.9050607@linux.intel.com>
Date:	Tue, 29 Jun 2010 11:41:17 -0700
From:	Arjan van de Ven <arjan@...ux.intel.com>
To:	Tejun Heo <tj@...nel.org>
CC:	Frederic Weisbecker <fweisbec@...il.com>,
	torvalds@...ux-foundation.org, mingo@...e.hu,
	linux-kernel@...r.kernel.org, jeff@...zik.org,
	akpm@...ux-foundation.org, rusty@...tcorp.com.au,
	cl@...ux-foundation.org, dhowells@...hat.com, oleg@...hat.com,
	axboe@...nel.dk, dwalker@...eaurora.org, stefanr@...6.in-berlin.de,
	florian@...kler.org, andi@...stfloor.org, mst@...hat.com,
	randy.dunlap@...cle.com, Arjan van de Ven <arjan@...radead.org>
Subject: Re: [PATCH 34/35] async: use workqueue for worker pool

On 6/29/2010 11:34 AM, Tejun Heo wrote:
> Hello,
>
> On 06/29/2010 08:22 PM, Arjan van de Ven wrote:
>    
>> I'm not trying to suggest "unbound".  I'm trying to suggest "don't
>> start bounding until you hit # threads>= # cpus you have some
>> clever tricks to deal with bounding things; but lets make sure that
>> the simple case of having less work to run in parallel than the
>> number of cpus gets dealt with simple and unbound.
>>      
> Well, the thing is, for most cases, binding to cpus is simply better.
>    

depends on the user.

For "throw over the wall" work, this is unclear.
Especially in the light of hyperthreading (sharing L1 cache) or even 
modern cpus (where many cores share a fast L3 cache).

I'm fine with a solution that has the caller say 'run anywhere' vs 'try 
to run local'.
I suspect there will be many many cases of 'run anywhere'.isn't hard at 
all. I just wanna know whether it's something which is

> actually useful.  So, where would that be useful?
>    

I think it's useful for all users of your worker pool, not (just) async.

it's a severe limitation of the current linux infrastructure, and your 
infrastructure has the chance to fix this...

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