On Friday, March 09, 2012, Kevin Hilman wrote: > "Rafael J. Wysocki" <rjw@xxxxxxx> writes: > > > On Thursday, March 08, 2012, Kevin Hilman wrote: > >> "Rafael J. Wysocki" <rjw@xxxxxxx> writes: > >> > >> > On Thursday, March 08, 2012, Kevin Hilman wrote: > >> >> "Rafael J. Wysocki" <rjw@xxxxxxx> writes: > >> >> > >> >> > From: Rafael J. Wysocki <rjw@xxxxxxx> > >> >> > > >> >> > A runtime suspend of a device (e.g. an MMC controller) belonging to > >> >> > a power domain or, in a more complicated scenario, a runtime suspend > >> >> > of another device in the same power domain, may cause power to be > >> >> > removed from the entire domain. In that case, the amount of time > >> >> > necessary to runtime-resume the given device (e.g. the MMC > >> >> > controller) is often substantially greater than the time needed to > >> >> > run its driver's runtime resume callback. That may hurt performance > >> >> > in some situations, because user data may need to wait for the > >> >> > device to become operational, so we should make it possible to > >> >> > prevent that from happening. > >> >> > > >> >> > For this reason, introduce a new sysfs attribute for devices, > >> >> > power/pm_qos_latency_us, allowing user space to specify the upper > >> >> > >> >> If we're expecting to have more of these knobs, maybe having a pm_qos > >> >> subdir under power will keep down the clutter in /sys/devices/.../power. > >> >> This knob would then be /sys/devices/.../power/pm_qos/pm_qos_latency_us. > >> > > >> > I'm not sure how difficult it is to create a subdir in sysfs under something > >> > that is not a kobject. > >> > > >> > Besides, this follows the convention already used by wakeup and runtime PM > >> > attributes that don't have their own subdirs (although there may be a number > >> > of them in each category). > >> > >> OK > >> > >> >> I think 'latency' alone is a bit too vague (wakeup latency? interrupt > >> >> latency? I think wakeup latency is clearer. Another possibility is > >> >> resume latency, IMO, that will lead to confusion about whether this > >> >> field also affects system suspend/resume. > >> > > >> > I think "wakeup latency" will lead to more confusion because of the > >> > wakeup-related attributes. > >> > >> What confusion? All of those are related to device wakeups from some > >> low power state, and so is this proposed latency attribute. So I don't > >> understand the potential confusion. > > > > The word "wakeup" may refer to many different things, as well as the word > > "resume". :-) > > Yes, but what's the confusion in this case? > > IMO, The existing /sys/devices/.../power/wakeup* meaning is the same > meaning as as for the wakeup latency in this patch, No, it is not. They refer to system wakeup. :-) > so I don't understand where the confusion would be. See above. ;-) Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
