On 2 March 2017 at 16:45, Patrick Bellasi <patrick.bell...@arm.com> wrote: > The current version of schedutil has some issues related to the management > of update flags used by systems with frequency domains spawning multiple CPUs. > > Each time a CPU utilisation update is issued by the scheduler a set of flags > are configured to define (mainly) which class is asking for a utilisation > update. These flags are then used by the frequency selection policy to > identify the OPP to choose. > > In the current implementation, CPU flags are overridden each time the > scheduler calls schedutil for an update. Such a behaviour produces issues > in these scenarios, where we assume CPU1 and CPU2 share the same frequency > domain: > a) a RT task which executed on CPU1 can keep the domain at an high frequency > for a long period of time, even if there are no longer RT tasks on > CPUs in that domain
Normally this is dropped after a tick. Nevertheless, there is an issue if the freq_update_delay_ns is shorter than a tick because of sugov RT thread > b) a FAIR task co-scheduled in the same CPU of a RT task can override the > flags configured by the RT task and potentially this can cause an > unwanted frequency drop > > These misbehaviours have been verified using a set of simple rt-app based > synthetic workloads, running on a ARM's Juno board, and results are > available in this Notebook [1]. > > This series proposes a set of fixes for the aforementioned issues as well > as a small improvement to speedup the selection of the maximum frequency > when RT tasks enter a CPU. > > This series is based on top of today's tip/sched/core and is public available > from this repository: > > git://www.linux-arm.com/linux-pb eas/schedutil/flags_fixes > > Cheers Patrick > > [1] https://gist.github.com/d6a21b459a18091b2b058668a550010d > > Patrick Bellasi (6): > cpufreq: schedutil: reset sg_cpus's flags at IDLE enter > cpufreq: schedutil: ignore the sugov kthread for frequencies > selections > cpufreq: schedutil: ensure max frequency while running RT/DL tasks > cpufreq: schedutil: relax rate-limiting while running RT/DL tasks > cpufreq: schedutil: avoid utilisation update when not necessary > sched/rt: fast switch to maximum frequency when RT tasks are scheduled > > include/linux/sched.h | 1 + > kernel/sched/cpufreq_schedutil.c | 59 > ++++++++++++++++++++++++++++++++++------ > kernel/sched/idle_task.c | 4 +++ > kernel/sched/rt.c | 15 ++++++++-- > 4 files changed, 68 insertions(+), 11 deletions(-) > > -- > 2.7.4 >
