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

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Date:	Mon, 25 Jun 2007 20:52:34 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Jonathan Corbet <corbet@....net>
Cc:	Ingo Molnar <mingo@...e.hu>, 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,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [RFC PATCH 0/6] Convert all tasklets to workqueues

On Mon, 2007-06-25 at 18:00 -0600, Jonathan Corbet wrote:
> A couple of days ago I said:
> 
> > The cafe_ccic (OLPC) camera driver uses a tasklet to move frames out of
> > the DMA buffers in the streaming I/O path....
> > 
> > Obviously some testing is called for here.  I will make an attempt to do
> > that testing
> 
> I've done that testing - I have an OLPC B3 unit running V2 of the
> tasklet->workqueue patch, and all seems well.  30 FPS to the display and
> no dropped frames.  The tasklets/0 process is running 3-5% CPU, in case
> that's interesting.  For whatever reason, I see about 3% *more* idle
> time when running just mplayer than I did without the patch.
> 
> Consider my minor qualms withdrawn, there doesn't seem to be any trouble
> in this area.

Jon, thanks a lot!

This is great news. I wonder if converting tasklets to work queues also
helps with other softirqs.  Before, softirqs could not preempt a
tasklet, since tasklets run as a softirq. With tasklets as work queues,
what's left as a softirq can now preempt tasklets. Perhaps this can even
help with performance.

-- Steve
  

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