Messages in this thread Patch in this message | | | From | Michael Turquette <> | Subject | Re: [RFCv5 PATCH 41/46] sched/fair: add triggers for OPP change requests | Date | Wed, 08 Jul 2015 08:42:15 -0700 |
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Hi Juri,
Quoting Morten Rasmussen (2015-07-07 11:24:24) > From: Juri Lelli <juri.lelli@arm.com> > > Each time a task is {en,de}queued we might need to adapt the current > frequency to the new usage. Add triggers on {en,de}queue_task_fair() for > this purpose. Only trigger a freq request if we are effectively waking up > or going to sleep. Filter out load balancing related calls to reduce the > number of triggers. > > cc: Ingo Molnar <mingo@redhat.com> > cc: Peter Zijlstra <peterz@infradead.org> > > Signed-off-by: Juri Lelli <juri.lelli@arm.com> > --- > kernel/sched/fair.c | 42 ++++++++++++++++++++++++++++++++++++++++-- > 1 file changed, 40 insertions(+), 2 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index f74e9d2..b8627c6 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -4281,7 +4281,10 @@ static inline void hrtick_update(struct rq *rq) > } > #endif > > +static unsigned int capacity_margin = 1280; /* ~20% margin */
This is a 25% margin. Calling it ~20% is a bit misleading :)
Should margin be scaled for cpus that do not have max capacity == 1024? In other words, should margin be dynamically calculated to be 20% of *this* cpu's max capacity?
I'm imagining a corner case where a heterogeneous cpu system is set up in such a way that adding margin that is hard-coded to 25% of 1024 almost always puts req_cap to the highest frequency, skipping some reasonable capacity states in between.
> + > static bool cpu_overutilized(int cpu); > +static unsigned long get_cpu_usage(int cpu); > struct static_key __sched_energy_freq __read_mostly = STATIC_KEY_INIT_FALSE; > > /* > @@ -4332,6 +4335,26 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags) > if (!task_new && !rq->rd->overutilized && > cpu_overutilized(rq->cpu)) > rq->rd->overutilized = true; > + /* > + * We want to trigger a freq switch request only for tasks that > + * are waking up; this is because we get here also during > + * load balancing, but in these cases it seems wise to trigger > + * as single request after load balancing is done. > + * > + * XXX: how about fork()? Do we need a special flag/something > + * to tell if we are here after a fork() (wakeup_task_new)? > + * > + * Also, we add a margin (same ~20% used for the tipping point) > + * to our request to provide some head room if p's utilization > + * further increases. > + */ > + if (sched_energy_freq() && !task_new) { > + unsigned long req_cap = get_cpu_usage(cpu_of(rq)); > + > + req_cap = req_cap * capacity_margin > + >> SCHED_CAPACITY_SHIFT;
Probably a dumb question:
Can we "cheat" here and just assume that capacity and load use the same units? That would avoid the multiplication and change your code to the following:
#define capacity_margin SCHED_CAPACITY_SCALE >> 2; /* 25% */ req_cap += SCHED_CAPACITY_SCALE;
> + cpufreq_sched_set_cap(cpu_of(rq), req_cap); > + } > } > hrtick_update(rq); > } > @@ -4393,6 +4416,23 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags) > if (!se) { > sub_nr_running(rq, 1); > update_rq_runnable_avg(rq, 1); > + /* > + * We want to trigger a freq switch request only for tasks that > + * are going to sleep; this is because we get here also during > + * load balancing, but in these cases it seems wise to trigger > + * as single request after load balancing is done. > + * > + * Also, we add a margin (same ~20% used for the tipping point) > + * to our request to provide some head room if p's utilization > + * further increases. > + */ > + if (sched_energy_freq() && task_sleep) { > + unsigned long req_cap = get_cpu_usage(cpu_of(rq)); > + > + req_cap = req_cap * capacity_margin > + >> SCHED_CAPACITY_SHIFT; > + cpufreq_sched_set_cap(cpu_of(rq), req_cap);
Filtering out the load_balance bits is neat.
Regards, Mike
> + } > } > hrtick_update(rq); > } > @@ -4959,8 +4999,6 @@ static int find_new_capacity(struct energy_env *eenv, > return idx; > } > > -static unsigned int capacity_margin = 1280; /* ~20% margin */ > - > static bool cpu_overutilized(int cpu) > { > return (capacity_of(cpu) * 1024) < > -- > 1.9.1 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/
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