On 31 May 2017 at 11:40, Peter Zijlstra <[email protected]> wrote: > On Wed, May 24, 2017 at 11:00:51AM +0200, Vincent Guittot wrote: >> schedutil governor relies on cfs_rq's util_avg to choose the OPP when cfs >> tasks are running. When the CPU is overloaded by cfs and rt tasks, cfs tasks >> are preempted by rt tasks and in this case util_avg reflects the remaining >> capacity that is used by cfs tasks but not what cfs tasks want to use. In >> such >> case, schedutil can select a lower OPP when cfs task runs whereas the CPU is >> overloaded. In order to have a more accurate view of the utilization of the >> CPU, we track the utilization that is used by RT tasks. >> DL tasks are not taken into account as they have their own utilization >> tracking mecanism. > > Well, the DL tracking is fairly pessimistic; it assumes all DL tasks > will consume their total budget, which will rarely, if ever, happen. > > So I suspect it might well be worth it to also track DL activity for the > purpose of compensating CFS. > > In fact, I don't think you particularly care about RT here, as anything > !CFS that preempts it, including those interrupts you mentioned. Which > gets us back to what rt_avg is. > >> We don't use rt_avg which doesn't have the same dynamic as PELT and which >> can include IRQ time that are also accounted in cfs task utilization > > Well, if rt_avg includes IRQ time, then that IRQ time is not part of > the task clock.
ah yes you're right. I haven't noticed irq time was removed from the clock used for accounting PELT > >> Signed-off-by: Vincent Guittot <[email protected]> >> --- >> >> If the changes are reasonnable, it might worth moving the PELT function in a >> dedicated pelt.c file and the ugly >> extern int update_rt_rq_load_avg(u64 now, int cpu, struct rt_rq *rt_rq, int >> running); >> in a pelt.h header >> >> >> kernel/sched/fair.c | 21 +++++++++++++++++++++ >> kernel/sched/rt.c | 9 +++++++++ >> kernel/sched/sched.h | 3 +++ >> 3 files changed, 33 insertions(+) > > Also, and I didn't check this, it is important that the windows are > aligned if you want to sum the values. yes. good point
