Messages in this thread | | | From | Vincent Guittot <> | Date | Mon, 29 Aug 2022 12:13:26 +0200 | Subject | Re: [RFC PATCH 1/1] sched/pelt: Introduce PELT multiplier |
| |
On Mon, 29 Aug 2022 at 12:03, Peter Zijlstra <peterz@infradead.org> wrote: > > On Mon, Aug 29, 2022 at 10:08:13AM +0200, Peter Zijlstra wrote: > > On Mon, Aug 29, 2022 at 07:54:50AM +0200, Dietmar Eggemann wrote: > > > From: Vincent Donnefort <vincent.donnefort@arm.com> > > > > > > The new sysctl sched_pelt_multiplier allows a user to set a clock > > > multiplier to x2 or x4 (x1 being the default). This clock multiplier > > > artificially speeds up PELT ramp up/down similarly to use a faster > > > half-life than the default 32ms. > > > > > > - x1: 32ms half-life > > > - x2: 16ms half-life > > > - x4: 8ms half-life > > > > > > Internally, a new clock is created: rq->clock_task_mult. It sits in the > > > clock hierarchy between rq->clock_task and rq->clock_pelt. > > > > > > Signed-off-by: Vincent Donnefort <vincent.donnefort@arm.com> > > > Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com> > > > > > +extern unsigned int sched_pelt_lshift; > > > + > > > +/* > > > + * absolute time |1 |2 |3 |4 |5 |6 | > > > + * @ mult = 1 --------****************--------****************- > > > + * @ mult = 2 --------********----------------********--------- > > > + * @ mult = 4 --------****--------------------****------------- > > > + * clock task mult > > > + * @ mult = 2 | | |2 |3 | | | | |5 |6 | | | > > > + * @ mult = 4 | | | | |2|3| | | | | | | | | | |5|6| | | | | | | > > > + * > > > + */ > > > +static inline void update_rq_clock_task_mult(struct rq *rq, s64 delta) > > > +{ > > > + delta <<= READ_ONCE(sched_pelt_lshift); > > > + > > > + rq->clock_task_mult += delta; > > > + > > > + update_rq_clock_pelt(rq, delta); > > > +} > > > > Hurmph... I'd almost go write you something like > > static_call()/static_branch() but for immediates. > > > > That said; given there's only like 3 options, perhaps a few > > static_branch() instances work just fine ? > > Also, I'm not at all sure about exposing that as an official sysctl.
Me too, I would even make it a boot time parameter so we can remove the new clock_task_mult clock and left shift clock_taslk or the delta before passing it to clock_pelt
> > How about something like so? > > --- > Subject: sched/pelt: Introduce PELT multiplier > From: Vincent Donnefort <vincent.donnefort@arm.com> > Date: Mon, 29 Aug 2022 07:54:50 +0200 > > From: Vincent Donnefort <vincent.donnefort@arm.com> > > The new sysctl sched_pelt_multiplier allows a user to set a clock > multiplier to x2 or x4 (x1 being the default). This clock multiplier > artificially speeds up PELT ramp up/down similarly to use a faster > half-life than the default 32ms. > > - x1: 32ms half-life > - x2: 16ms half-life > - x4: 8ms half-life > > Internally, a new clock is created: rq->clock_task_mult. It sits in the > clock hierarchy between rq->clock_task and rq->clock_pelt. > > [peterz: Use sched_feat()] > Signed-off-by: Vincent Donnefort <vincent.donnefort@arm.com> > Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> > --- > kernel/sched/core.c | 2 +- > kernel/sched/features.h | 3 +++ > kernel/sched/pelt.h | 45 +++++++++++++++++++++++++++++++++++++++++---- > kernel/sched/sched.h | 1 + > 4 files changed, 46 insertions(+), 5 deletions(-) > > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -727,7 +727,7 @@ static void update_rq_clock_task(struct > if ((irq_delta + steal) && sched_feat(NONTASK_CAPACITY)) > update_irq_load_avg(rq, irq_delta + steal); > #endif > - update_rq_clock_pelt(rq, delta); > + update_rq_clock_task_mult(rq, delta); > } > > void update_rq_clock(struct rq *rq) > --- a/kernel/sched/features.h > +++ b/kernel/sched/features.h > @@ -101,3 +101,6 @@ SCHED_FEAT(LATENCY_WARN, false) > > SCHED_FEAT(ALT_PERIOD, true) > SCHED_FEAT(BASE_SLICE, true) > + > +SCHED_FEAT(PELT_M2, false) > +SCHED_FEAT(PELT_M4, false) > --- a/kernel/sched/pelt.h > +++ b/kernel/sched/pelt.h > @@ -61,6 +61,14 @@ static inline void cfs_se_util_change(st > WRITE_ONCE(avg->util_est.enqueued, enqueued); > } > > +static inline u64 rq_clock_task_mult(struct rq *rq) > +{ > + lockdep_assert_rq_held(rq); > + assert_clock_updated(rq); > + > + return rq->clock_task_mult; > +} > + > static inline u64 rq_clock_pelt(struct rq *rq) > { > lockdep_assert_rq_held(rq); > @@ -72,7 +80,7 @@ static inline u64 rq_clock_pelt(struct r > /* The rq is idle, we can sync to clock_task */ > static inline void _update_idle_rq_clock_pelt(struct rq *rq) > { > - rq->clock_pelt = rq_clock_task(rq); > + rq->clock_pelt = rq_clock_task_mult(rq); > > u64_u32_store(rq->clock_idle, rq_clock(rq)); > /* Paired with smp_rmb in migrate_se_pelt_lag() */ > @@ -121,6 +129,30 @@ static inline void update_rq_clock_pelt( > rq->clock_pelt += delta; > } > > +extern unsigned int sched_pelt_lshift; > + > +/* > + * absolute time |1 |2 |3 |4 |5 |6 | > + * @ mult = 1 --------****************--------****************- > + * @ mult = 2 --------********----------------********--------- > + * @ mult = 4 --------****--------------------****------------- > + * clock task mult > + * @ mult = 2 | | |2 |3 | | | | |5 |6 | | | > + * @ mult = 4 | | | | |2|3| | | | | | | | | | |5|6| | | | | | | > + * > + */ > +static inline void update_rq_clock_task_mult(struct rq *rq, s64 delta) > +{ > + if (sched_feat(PELT_M2)) > + delta *= 2; > + if (sched_feat(PELT_M4)) > + delta *= 4; > + > + rq->clock_task_mult += delta; > + > + update_rq_clock_pelt(rq, delta); > +} > + > /* > * When rq becomes idle, we have to check if it has lost idle time > * because it was fully busy. A rq is fully used when the /Sum util_sum > @@ -147,7 +179,7 @@ static inline void update_idle_rq_clock_ > * rq's clock_task. > */ > if (util_sum >= divider) > - rq->lost_idle_time += rq_clock_task(rq) - rq->clock_pelt; > + rq->lost_idle_time += rq_clock_task_mult(rq) - rq->clock_pelt; > > _update_idle_rq_clock_pelt(rq); > } > @@ -218,13 +250,18 @@ update_irq_load_avg(struct rq *rq, u64 r > return 0; > } > > -static inline u64 rq_clock_pelt(struct rq *rq) > +static inline u64 rq_clock_task_mult(struct rq *rq) > { > return rq_clock_task(rq); > } > > +static inline u64 rq_clock_pelt(struct rq *rq) > +{ > + return rq_clock_task_mult(rq); > +} > + > static inline void > -update_rq_clock_pelt(struct rq *rq, s64 delta) { } > +update_rq_clock_task_mult(struct rq *rq, s64 delta) { } > > static inline void > update_idle_rq_clock_pelt(struct rq *rq) { } > --- a/kernel/sched/sched.h > +++ b/kernel/sched/sched.h > @@ -1009,6 +1009,7 @@ struct rq { > u64 clock; > /* Ensure that all clocks are in the same cache line */ > u64 clock_task ____cacheline_aligned; > + u64 clock_task_mult; > u64 clock_pelt; > unsigned long lost_idle_time; > u64 clock_pelt_idle;
| |