"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. Kevin -- 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
