On Mon, Jul 16, 2018 at 09:28:55AM +0100, Patrick Bellasi wrote: > The SCHED_DEADLINE scheduling class provides an advanced and formal > model to define tasks requirements which can be translated into proper > decisions for both task placements and frequencies selections. > Other classes have a more simplified model which is essentially based on > the relatively simple concept of POSIX priorities. > > Such a simple priority based model however does not allow to exploit > some of the most advanced features of the Linux scheduler like, for > example, driving frequencies selection via the schedutil cpufreq > governor. However, also for non SCHED_DEADLINE tasks, it's still > interesting to define tasks properties which can be used to better > support certain scheduler decisions. > > Utilization clamping aims at exposing to user-space a new set of > per-task attributes which can be used to provide the scheduler with some > hints about the expected/required utilization for a task. > This will allow to implement a more advanced per-task frequency control > mechanism which is not based just on a "passive" measured task > utilization but on a more "active" approach. For example, it could be > possible to boost interactive tasks, thus getting better performance, or > cap background tasks, thus being more energy efficient. > Ultimately, such a mechanism can be considered similar to the cpufreq's > powersave, performance and userspace governor but with a much fine > grained and per-task control. > > Let's introduce a new API to set utilization clamping values for a > specified task by extending sched_setattr, a syscall which already > allows to define task specific properties for different scheduling > classes. > Specifically, a new pair of attributes allows to specify a minimum and > maximum utilization which the scheduler should consider for a task. > > Signed-off-by: Patrick Bellasi <[email protected]> > Cc: Ingo Molnar <[email protected]> > Cc: Peter Zijlstra <[email protected]> > Cc: Tejun Heo <[email protected]> > Cc: Rafael J. Wysocki <[email protected]> > Cc: Vincent Guittot <[email protected]> > Cc: Viresh Kumar <[email protected]> > Cc: Paul Turner <[email protected]> > Cc: Todd Kjos <[email protected]> > Cc: Joel Fernandes <[email protected]> > Cc: Steve Muckle <[email protected]> > Cc: Juri Lelli <[email protected]> > Cc: Dietmar Eggemann <[email protected]> > Cc: Morten Rasmussen <[email protected]> > Cc: [email protected] > Cc: [email protected] > --- > include/linux/sched.h | 16 ++++++++ > include/uapi/linux/sched.h | 4 +- > include/uapi/linux/sched/types.h | 64 +++++++++++++++++++++++++++----- > init/Kconfig | 19 ++++++++++ > kernel/sched/core.c | 39 +++++++++++++++++++ > 5 files changed, 132 insertions(+), 10 deletions(-) > > diff --git a/include/linux/sched.h b/include/linux/sched.h > index 43731fe51c97..fd8495723088 100644 > --- a/include/linux/sched.h > +++ b/include/linux/sched.h > @@ -279,6 +279,17 @@ struct vtime { > u64 gtime; > }; > > +enum uclamp_id { > + /* No utilization clamp group assigned */ > + UCLAMP_NONE = -1, > + > + UCLAMP_MIN = 0, /* Minimum utilization */ > + UCLAMP_MAX, /* Maximum utilization */ > + > + /* Utilization clamping constraints count */ > + UCLAMP_CNT > +}; > + > struct sched_info { > #ifdef CONFIG_SCHED_INFO > /* Cumulative counters: */ > @@ -649,6 +660,11 @@ struct task_struct { > #endif > struct sched_dl_entity dl; > > +#ifdef CONFIG_UCLAMP_TASK > + /* Utlization clamp values for this task */ > + int uclamp[UCLAMP_CNT]; > +#endif
Seems a bit wasteful to me. Seems you need 2 values that are in the range 0..1024. Can we not do better with task_struct space usage? thanks! - Joel
