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

Florian Mickler
2010-06-03T14:18:24Z

On Thu, 03 Jun 2010 08:24:31 -0500
James Bottomley <James.Bottomley@suse.de> 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