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

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Date:	Mon, 25 Jun 2007 13:06:43 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Tilman Schmidt <tilman@...p.cc>
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 18:50 +0200, Tilman Schmidt wrote:

> The Siemens Gigaset ISDN base driver uses tasklets in its isochronous
> data paths. These will be scheduled for each completion of an isochronous
> URB, or every 8 msec for each of the four isochronous pipes if both B
> channels are connected. The driver uses three URBs for each pipe, always
> maintaining two in flight while processing the third one. So the tasklet
> has to run within 16 ms from being scheduled in order to avoid packet
> loss (in the receive path) or data underrun (in the transmit path).
> 
> Does that qualify as performance sensitive for the purpose of this
> discussion?

Actually, no.  16ms, even 8ms is an incredible amount of time. Unless
you have a thread that is running at a higher priority than the thread
that handles the work queue performing the task, you would have no
problems making that deadline.  If you did miss the deadline without
having ridiculously high prio tasks, I would think that you would miss
your deadline with tasklets as well. Unless the large latency has to do
with preempt_disable, but that large of a latency would be IMHO a bug.

-- Steve
 

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