linux-kernel - Re: init's children list is long and slows reaping children.

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Message-ID: <461B59F5.6060300@garzik.org>
Date:	Tue, 10 Apr 2007 05:33:41 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Jones <davej@...hat.com>, Robin Holt <holt@....com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Jack Steiner <steiner@...ricas.sgi.com>
Subject: Re: init's children list is long and slows reaping children.

Ingo Molnar wrote:
> * Russell King <rmk+lkml@....linux.org.uk> wrote:
> 
>> One per PC card socket to avoid the sysfs locking crappyness that 
>> would otherwise deadlock, and to convert from the old unreadable state 
>> machine implementation to a much more readable linearly coded 
>> implementation.
>>
>> Could probably be eliminated if we had some mechanism to spawn a 
>> helper thread to do some task as required which didn't block other 
>> helper threads until it completes.
> 
> looks like the perfect usecase for threadlets. (threadlets only use up a 
> separate context if necessary and can be coded in the familiar 
> sequential/linear model)

Same response as to Andrew:  AFAICS that just increases complexity.

The simple path for programmers is writing straightforward code that 
does something like

	blah
	msleep()
	blah

or in pccardd's case,

	mutex_lock()
	blah
	mutex_unlock()

to permit sleeping without having to write more-complex code that deals 
with context transitions.

For slow-path, infrequently executed code, it is best to keep it as 
simple as possible.

	Jeff


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