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SubjectRe: linux-next: workqueues tree build failure
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


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