From: Takashi Iwai <tiwai@suse•de>
To: Tejun Heo <tj@kernel•org>
Cc: Peter Ujfalusi <peter.ujfalusi@nokia•com>,
Stephen Rothwell <sfr@canb•auug.org.au>,
"linux-next@vger•kernel.org" <linux-next@vger•kernel.org>,
"linux-kernel@vger•kernel.org" <linux-kernel@vger•kernel.org>,
Mark Brown <broonie@opensource•wolfsonmicro.com>
Subject: Re: linux-next: workqueues tree build failure
Date: Thu, 26 Nov 2009 10:24:30 +0100 [thread overview]
Message-ID: <s5hzl69myep.wl%tiwai@suse.de> (raw)
In-Reply-To: <4B0E467A.8080201@kernel.org>
At Thu, 26 Nov 2009 18:12:26 +0900,
Tejun Heo wrote:
>
> Hello,
>
> 11/26/2009 05:16 PM, Peter Ujfalusi wrote:
> >> Takashi, RT workqueue is going away. Do you really need it?
> >
> > What can be used instead of RT workqueue?
> > The tlv320dac33 needs RT workqueue because I need to send the I2C
> > command with minimum delay to the codec. If this can not be done
> > (the workqueue is delayed), and the codec does not receive the
> > command in time, it will literally die. What are the options to
> > replace the RT workqueue?
>
> The problem with RT workqueue is that RT and queue don't really mix
> well. To act in real time, it requires all the resource pre-allocated
> and dedicated to it making queueing or pooling meaningless. The
> original workqueue code created dedicated pool of threads for each
> workqueue so it could be used for RT but new implementation uses
> shared worker pool, so it can't be used as an interface to dedicated
> threads.
>
> I haven't read the code but,
>
> * If you need to respond fast, wouldn't you be doing that from IRQ
> handler or softirq? Do you need task context?
>
> * Or is it that it's not triggered by IRQ but once the transfer
> started it can't be interrupted? But in this case preempt_disable()
> or local_irq_disable() should suffice.
The relevant code uses the workqueue as a sort of BH, just triggers
from the hard irq handler. If any, we may use a threaded handler or
so...
thanks,
Takashi
next prev parent reply other threads:[~2009-11-26 9:24 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-11-26 8:00 linux-next: workqueues tree build failure Stephen Rothwell
2009-11-26 8:04 ` Tejun Heo
2009-11-26 8:16 ` Peter Ujfalusi
2009-11-26 9:12 ` Tejun Heo
2009-11-26 9:24 ` Takashi Iwai [this message]
2009-11-26 9:31 ` Peter Ujfalusi
2009-11-26 10:18 ` Mark Brown
2009-11-26 11:44 ` Peter Ujfalusi
2009-11-26 12:49 ` Andy Walls
2009-11-26 13:23 ` Peter Ujfalusi
2009-11-26 12:40 ` Andy Walls
2009-11-26 12:56 ` Mark Brown
2009-11-27 2:02 ` Tejun Heo
2009-11-27 8:37 ` Takashi Iwai
2009-11-27 8:42 ` Tejun Heo
2009-11-27 10:09 ` Peter Ujfalusi
2009-11-27 11:38 ` Mark Brown
2009-11-27 13:50 ` Andy Walls
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