linux-kernel - Re: workqueue thing

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Message-ID: <4B31D5A7.2040608@kernel.org>
Date:	Wed, 23 Dec 2009 17:32:39 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>, awalls@...ix.net,
	linux-kernel@...r.kernel.org, jeff@...zik.org,
	akpm@...ux-foundation.org, jens.axboe@...cle.com,
	rusty@...tcorp.com.au, cl@...ux-foundation.org,
	dhowells@...hat.com, arjan@...ux.intel.com, avi@...hat.com,
	johannes@...solutions.net, andi@...stfloor.org
Subject: Re: workqueue thing

Hello, Ingo.

On 12/23/2009 05:12 PM, Ingo Molnar wrote:
> 
> * Ingo Molnar <mingo@...e.hu> wrote:
> 
>> At least as far as i'm concerned, i'd like to see actual uses. It's a big 
>> linecount increase all things considered:
>>
>>    20 files changed, 2783 insertions(+), 660 deletions(-)

BTW, the code contains way more comment afterwards and has other
benefits like not having crazy number of workers around on many core
machines.

>> and you say it _wont_ help performance/scalability (this aspect wasnt clear 

And I think it will help scalability for sure although it depends on
what type of scalability you're talking about.

>> to me from previous discussions), so the (yet to be seen) complexity 
>> reduction in other code ought to be worth it.
> 
> To further stress this point, i'd like to point to the very first commit that 
> introduced kernel/workqueue.c into Linux 7 years ago:
> 
>  | From 6ed12ff83c765aeda7d38d3bf9df7d46d24bfb11 Mon Sep 17 00:00:00 2001
>  | From: Ingo Molnar <mingo@...e.hu>
>  | Date: Mon, 30 Sep 2002 22:17:42 -0700
>  | Subject: [PATCH] [PATCH] Workqueue Abstraction
> 
> look at the diffstat of that commit:
> 
>    201 files changed, 1102 insertions(+), 1194 deletions(-)
> 
> despite adding a new abstraction and kernel subsystem (workqueues), that 
> commit modified more than a hundred drivers to make use of it, and managed to 
> achieve a net linecount decrease of 92 lines - despite adding hundreds of 
> lines of a new core facility.
> 
> Likewise, for this particular patchset it should be possible to identify 
> existing patterns of code in the existing code base of 6+ millions lines of 
> Linux driver code that would make the advantages of this +2000 lines of core 
> kernel code plain obvious. There were multipe claims of problems with the 
> current abstractions - so there sure must be a way to show off the new code in

I'm not sure I'm gonna update that many places in a single sweep but
yeah let's give it a shot.

Thanks.

-- 
tejun
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