Messages in this thread | | | Subject | Re: [PATCH 4/4] cpuidle/menu: add per cpu pm_qos_resume_latency consideration | From | "Rafael J. Wysocki" <> | Date | Fri, 23 Sep 2016 03:36:30 +0200 |
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On 9/14/2016 10:28 AM, Vincent Guittot wrote: > Hi Rafael, > > On 14 September 2016 at 00:10, Rafael J. Wysocki <rjw@rjwysocki.net> wrote: >> On Tuesday, September 13, 2016 10:02:49 PM Alex Shi wrote: >>> Hi Daniel & Rafael, >>> >>> Any comments on this patch? >> I actually am not sure about the whole series. >> >> I know your motivation, but honestly the changes here may not be the best way >> to achieve what you need. >> >> You may think that the changes are trivial, but in fact they are not. There >> are side effects and I'm not sure about the resulting user space interface >> at all. > This patchset has got 2 parts: > - one part is about taking into account per-device resume latency > constraint when selecting the idle state of a CPU. This value can > already be set by kernel (even if it's probably not done yet) but this > constraint is never taken into account > - the other part is about exposing the resume latency to userspace. > This part might raise more discussion but I see one example that could > take advantage of this. When you have several clusters of CPUs and you > want to dedicate some CPUs to latency sensitive activity and prevent > deep sleep state on these CPUs but you want to let the other CPUs > using all C-state
The first very basic question about this I have is whether or not the device PM QoS mechanism is suitable for the task at hand at all.
It certainly hasn't been invented with it in mind.
Thanks, Rafael
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