Re: [linux-pm] [PATCH 0/8] Suspend block api (version 8)

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On Thu, 03 Jun 2010 08:24:31 -0500
James Bottomley <James.Bottomley@xxxxxxx> 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)?

I think schedule_work() (worqueue.h) can take care of that. 
Thats how the rfkill subsystem does it. 

Cheers,
Flo
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