"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. > I'll go for "resume_latency" if you don't mind. :-) Most people think of resume as coming back from system PM. If this is called resume_latency, I would expect confusion about why setting this attribute has no effect on how fast their system returns from system suspend. Kevin -- 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
