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

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Date:	Fri, 22 Jun 2007 18:58:50 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Linus Torvalds <torvalds@...ux-foundation.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 23:59 +0200, Ingo Molnar wrote:
> * Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> 
> > If the numbers say that there is no performance difference (or even 
> > better: that the new code performs better or fixes some latency issue 
> > or whatever), I'll be very happy. But if the numbers say that it's 
> > worse, no amount of cleanliness really changes that.
> 
> Most of the tasklet uses are in rarely used or arcane drivers - in fact 
> none of my 10 test-boxes utilizes _any_ tasklet in any way that could 
> even get close to mattering to performance. In other words: i just 
> cannot test this, nor do i think that others will really test this. 

This is exactly why I included that CONFIG option in the first series.
Because, I only have a handful of hardware that actually uses tasklets.
And all those pr_debugs I had where turned on on most of my boxes.  I
was not flooded with prints either (every function including
tasklet_schedule had a print).

So, basically, I can't do benchmarks. I was hoping to get this into -mm
with a easy way for people, who have hardware that uses tasklets
extensively, to run it with tasklets on and off to see if there is a
difference.  My fear of not having a config option to switch between the
two (for -mm only) is that we may lose benchmarking from those that are
not comfortable at removing this patch from -mm.  There are people out
there that download and test the -mm tree straight from kernel.org.
Just because someone compiles their own kernel doesn't mean they can (or
will) patch it.

-- Steve

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