On 14/10/2020 16:50, Patrick Bellasi wrote: > > On Tue, Oct 13, 2020 at 22:25:48 +0200, Dietmar Eggemann > <dietmar.eggem...@arm.com> wrote...
[...] >> On 12/10/2020 18:31, Yun Hsiang wrote: [...] > Not sure what's the specific use-case Yun is after, but I have at least > one in my mind. > > Let say a task does not need boost at all, independently from > the cgroup it's configured to run into. We can go on and set its task > specific value to util_min=0. > > In this case, when the task is running alone on a CPU, it will get > always the minimum OPP, independently from its utilization. > > Now, after a while (e.g. some special event happens) we want to relax > this constraint and allow the task to run: > 1. at whatever OPP is required by its utilization > 2. with any additional boost possibly enforced by its cgroup > > Right now we have only quite cumbersome or hack solution: > a) go check the current cgroup util_min value and set for the task > something higher than that IMHO, it's not only the current taskgroup. You would have to check the whole hierarchy (including system-wide). > b) set task::util_min=1024 thus asking for the maximum possible boost > > Solution a) is more code for userspace and it's also racy. Solution b) > is misleading since the task does not really want to run at 1024. > It's also potentially over-killing in case the task should be moved to > the root group, which is normally unbounded and thus the task will get > executed always at the max OPP without any specific reason why. > > A simple _UCLAMP_RESET flag will allow user-space to easily switch a > tasks to the default behavior (follow utilization or recommended > boosts) which is what a task usually gets when it does not opt-in to > uclamp. OK, so restricting (eclipsing) 'user_defined' task uclamp values to taskgroup (hierarchy) values by setting the task value > the taskgroup (hierarchy) value is cumbersome. A task uclamp reset function will force this 'user_defined' task automatically under taskgroup (hierarchy) control by turning it into a '!user_defined' task again. ... and this will facilitate easier uclamp userspace controller.
