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 _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
