On Thu, 2010-06-03 at 09:58 -0700, Kevin Hilman wrote: > "Gross, Mark" <mark.gross@xxxxxxxxx> writes: > > >>-----Original Message----- > >>From: Kevin Hilman [mailto:khilman@xxxxxxxxxxxxxxxxxxx] > >>Sent: Thursday, June 03, 2010 7:43 AM > >>To: Peter Zijlstra > >>Cc: Alan Cox; Gross, Mark; Florian Mickler; James Bottomley; Arve > >>Hjønnevåg; Neil Brown; tytso@xxxxxxx; LKML; Thomas Gleixner; Linux OMAP > >>Mailing List; Linux PM; felipe.balbi@xxxxxxxxx > >>Subject: Re: [linux-pm] [PATCH 0/8] Suspend block api (version 8) > >> > >>Peter Zijlstra <peterz@xxxxxxxxxxxxx> writes: > >> > >>> 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) > >>> > >>> Why would the kernel change the QoS state of a task? Why not have two > >>> interacting QoS variables, one for the task, one for the subsystem in > >>> question, and the action depends on their relative value? > >> > >>Yes, having a QoS parameter per-subsystem (or even per-device) is very > >>important for SoCs that have independently controlled powerdomains. > >>If all devices/subsystems in a particular powerdomain have QoS > >>parameters that permit, the power state of that powerdomain can be > >>lowered independently from system-wide power state and power states of > >>other power domains. > >> > > This seems similar to that pm_qos generalization into bus drivers we where > > waving our hands at during the collab summit in April? We never did get > > into meaningful detail at that time. > > The hand-waving was around how to generalize it into the driver-model, > or PM QoS. We're already doing this for OMAP, but in an OMAP-specific > way, but it's become clear that this is something useful to > generalize. Do you have a pointer to the source and description? It might be useful to look at to do a reality check on what we're talking about. James -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
