linux-kernel - Re: workqueue thing

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Message-ID: <20091223081238.GA29963@elte.hu>
Date:	Wed, 23 Dec 2009 09:12:38 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Tejun Heo <tj@...nel.org>
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

* 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(-)
> 
> and you say it _wont_ help performance/scalability (this aspect wasnt clear 
> 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 
a few places.

	Ingo
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