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

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Date:	Fri, 22 Jun 2007 15:15:32 -0700
From:	Daniel Walker <dwalker@...sta.com>
To:	david@...g.hm
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, 2007-06-22 at 15:09 -0700, david@...g.hm wrote:
> 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.

For testing I'd agree, but not for a kernel that is suppose to be
stable.

> 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.

Since I've been working with -rt (~2 years now I think) it's clear that
the number of testers of the patch isn't all that high compared to the
stable kernel . There are tons of drivers which get no coverage by -rt
patch users.

So the fact that something similar is in -rt is good, but it's not a
silver bullet ..

Daniel

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