linux-kernel - Re: [RFC PATCH 0/6] Convert all tasklets to workqueues

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Message-ID: <Pine.LNX.4.64.0706221506560.14942@asgard.lang.hm>
Date:	Fri, 22 Jun 2007 15:09:21 -0700 (PDT)
From:	david@...g.hm
To:	Daniel Walker <dwalker@...sta.com>
cc:	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Christoph Hellwig <hch@...radead.org>,
	john stultz <johnstul@...ibm.com>,
	Oleg Nesterov <oleg@...sign.ru>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Dipankar Sarma <dipankar@...ibm.com>,
	"David S. Miller" <davem@...emloft.net>, matthew.wilcox@...com,
	kuznet@....inr.ac.ru
Subject: Re: [RFC PATCH 0/6] Convert all tasklets to workqueues

On Fri, 22 Jun 2007, Daniel Walker wrote:

> 
> On Fri, 2007-06-22 at 22:40 +0200, Ingo Molnar wrote:
>
>>
>>  - tasklets have certain fairness limitations. (they are executed in
>>    softirq context and thus preempt everything, even if there is some
>>    potentially more important, high-priority task waiting to be
>>    executed.)
>
> Since -rt has been executing tasklets in process context for a long
> time, I'm not sure this change would cause to many regressions. However,
> it seems like implicit dependencies on "tasklets preempt everything"
> might crop up. The other issue is if they don't "preempt
> everything" (most of the time), what default priority do we give them
> (all of the time)? It seems like Christoph's suggestion of converting
> all the tasklets individually might be a better option, to deal with
> specific pitfalls.

that would be the safe way to do it, but it will take a lot of time and a 
lot of testing.

it's probably better to try the big-bang change and only if you see 
problames go back and break things down.

remember, these changes have been in use in -rt for a while. there's 
reason to believe that they aren't going to cause drastic problems.

David Lang
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