"Rafael J. Wysocki" <rjw@xxxxxxx> writes: > 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. :-) OK, now I'm confused (again). I thought those could be used for runtime PM wakeups also. At least I was planning on using them for any kind of wakeup. >> so I don't understand where the confusion would be. > > See above. ;-) Sheesh, this is getting ugly. So wakeup* attributes refer to system resume and resume* attribues refer to runtime PM. Yuck. 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
