On Thu, 3 Jun 2010, James Bottomley wrote:
> On Thu, 2010-06-03 at 11:03 +0100, Alan Cox wrote:
> > > [mtg: ] This has been a pain point for the PM_QOS implementation. They
> > > change the constrain back and forth at the transaction level of the i2c
> > > driver. The pm_qos code really wasn't made to deal with such hot path
> > > use, as each such change triggers a re-computation of what the aggregate
> > > qos request is.
> >
> > That should be trivial in the usual case because 99% of the time you can
> > hot path
> >
> > the QoS entry changing is the latest one
> > there have been no other changes
> > If it is valid I can use the cached previous aggregate I cunningly
> > saved in the top QoS entry when I computed the new one
> >
> > (ie most of the time from the kernel side you have a QoS stack)
>
> It's not just the list based computation: that's trivial to fix, as you
> say ... the other problem is the notifier chain, because that's blocking
> and could be long. Could we invoke the notifier through a workqueue?
> It doesn't seem to have veto power, so it's pure notification, does it
> matter if the notice is delayed (as long as it's in order)?
It depends on the information type and for a lot of things we might
get away without notifiers.
The only real issue is when you need to get other cores out of their
deep idle state to make a new constraint work. That's what we do with
the DMA latency notifier right now.
Thanks,
tglx
--
To unsubscribe from this list: send the line "unsubscribe linux-omap" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
