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Date: Sat, 20 Jan 2024 13:22:03 +0530
From: Ashay Jaiswal <quic_ashayj@...cinc.com>
To: Qais Yousef <qyousef@...alina.io>, Ingo Molnar <mingo@...nel.org>,
"Peter
Zijlstra" <peterz@...radead.org>,
"Rafael J. Wysocki" <rafael@...nel.org>,
Viresh Kumar <viresh.kumar@...aro.org>,
Vincent Guittot
<vincent.guittot@...aro.org>,
Dietmar Eggemann <dietmar.eggemann@....com>
CC: <linux-kernel@...r.kernel.org>, <linux-pm@...r.kernel.org>,
Lukasz Luba
<lukasz.luba@....com>, Wei Wang <wvw@...gle.com>,
Rick Yiu
<rickyiu@...gle.com>, Chung-Kai Mei <chungkai@...gle.com>,
<quic_anshar@...cinc.com>, <quic_atulpant@...cinc.com>,
<quic_shashim@...cinc.com>, <quic_rgottimu@...cinc.com>,
<quic_adharmap@...cinc.com>, <quic_kshivnan@...cinc.com>,
<quic_pkondeti@...cinc.com>
Subject: Re: [PATCH v2 8/8] sched/pelt: Introduce PELT multiplier
Hello Qais Yousef,
We ran few benchmarks with PELT multiplier patch on a Snapdragon 8Gen2
based internal Android device and we are observing significant
improvements with PELT8 configuration compared to PELT32.
Following are some of the benchmark results with PELT32 and PELT8
configuration:
+-----------------+---------------+----------------+----------------+
| Test case | PELT32 | PELT8 |
+-----------------+---------------+----------------+----------------+
| | Overall | 711543 | 971275 |
| +---------------+----------------+----------------+
| | CPU | 193704 | 224378 |
| +---------------+----------------+----------------+
|ANTUTU V9.3.9 | GPU | 284650 | 424774 |
| +---------------+----------------+----------------+
| | MEM | 125207 | 160548 |
| +---------------+----------------+----------------+
| | UX | 107982 | 161575 |
+-----------------+---------------+----------------+----------------+
| | Single core | 1170 | 1268 |
|GeekBench V5.4.4 +---------------+----------------+----------------+
| | Multi core | 2530 | 3797 |
+-----------------+---------------+----------------+----------------+
| | Twitter | >50 Janks | 0 |
| SCROLL +---------------+----------------+----------------+
| | Contacts | >30 Janks | 0 |
+-----------------+---------------+----------------+----------------+
Please let us know if you need any support with running any further
workloads for PELT32/PELT8 experiments, we can help with running the
experiments.
Thank you,
Ashay Jaiswal
On 12/8/2023 5:53 AM, Qais Yousef wrote:
> From: Vincent Donnefort <vincent.donnefort@....com>
>
> The new sched_pelt_multiplier boot param 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.
>
> The param is set as read only and can only be changed at boot time via
>
> kernel.sched_pelt_multiplier=[1, 2, 4]
>
> PELT has a big impact on the overall system response and reactiveness to
> change. Smaller PELT HF means it'll require less time to reach the
> maximum performance point of the system when the system become fully
> busy; and equally shorter time to go back to lowest performance point
> when the system goes back to idle.
>
> This faster reaction impacts both dvfs response and migration time
> between clusters in HMP system.
>
> Smaller PELT values are expected to give better performance at the cost
> of more power. Under powered systems can particularly benefit from
> smaller values. Powerful systems can still benefit from smaller values
> if they want to be tuned towards perf more and power is not the major
> concern for them.
>
> This combined with respone_time_ms from schedutil should give the user
> and sysadmin a deterministic way to control the triangular power, perf
> and thermals for their system. The default response_time_ms will half
> as PELT HF halves.
>
> Update approximate_{util_avg, runtime}() to take into account the PELT
> HALFLIFE multiplier.
>
> Signed-off-by: Vincent Donnefort <vincent.donnefort@....com>
> Signed-off-by: Dietmar Eggemann <dietmar.eggemann@....com>
> [Converted from sysctl to boot param and updated commit message]
> Signed-off-by: Qais Yousef (Google) <qyousef@...alina.io>
> ---
> kernel/sched/core.c | 2 +-
> kernel/sched/pelt.c | 52 ++++++++++++++++++++++++++++++++++++++++++--
> kernel/sched/pelt.h | 42 +++++++++++++++++++++++++++++++----
> kernel/sched/sched.h | 1 +
> 4 files changed, 90 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index b4a1c8ea9e12..9c8626b4ddff 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -745,7 +745,7 @@ static void update_rq_clock_task(struct rq *rq, s64 delta)
> 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)
> diff --git a/kernel/sched/pelt.c b/kernel/sched/pelt.c
> index 00a1b9c1bf16..0a10e56f76c7 100644
> --- a/kernel/sched/pelt.c
> +++ b/kernel/sched/pelt.c
> @@ -468,6 +468,54 @@ int update_irq_load_avg(struct rq *rq, u64 running)
> }
> #endif /* CONFIG_HAVE_SCHED_AVG_IRQ */
>
> +__read_mostly unsigned int sched_pelt_lshift;
> +static unsigned int sched_pelt_multiplier = 1;
> +
> +static int set_sched_pelt_multiplier(const char *val, const struct kernel_param *kp)
> +{
> + int ret;
> +
> + ret = param_set_int(val, kp);
> + if (ret)
> + goto error;
> +
> + switch (sched_pelt_multiplier) {
> + case 1:
> + fallthrough;
> + case 2:
> + fallthrough;
> + case 4:
> + WRITE_ONCE(sched_pelt_lshift,
> + sched_pelt_multiplier >> 1);
> + break;
> + default:
> + ret = -EINVAL;
> + goto error;
> + }
> +
> + return 0;
> +
> +error:
> + sched_pelt_multiplier = 1;
> + return ret;
> +}
> +
> +static const struct kernel_param_ops sched_pelt_multiplier_ops = {
> + .set = set_sched_pelt_multiplier,
> + .get = param_get_int,
> +};
> +
> +#ifdef MODULE_PARAM_PREFIX
> +#undef MODULE_PARAM_PREFIX
> +#endif
> +/* XXX: should we use sched as prefix? */
> +#define MODULE_PARAM_PREFIX "kernel."
> +module_param_cb(sched_pelt_multiplier, &sched_pelt_multiplier_ops, &sched_pelt_multiplier, 0444);
> +MODULE_PARM_DESC(sched_pelt_multiplier, "PELT HALFLIFE helps control the responsiveness of the system.");
> +MODULE_PARM_DESC(sched_pelt_multiplier, "Accepted value: 1 32ms PELT HALIFE - roughly 200ms to go from 0 to max performance point (default).");
> +MODULE_PARM_DESC(sched_pelt_multiplier, " 2 16ms PELT HALIFE - roughly 100ms to go from 0 to max performance point.");
> +MODULE_PARM_DESC(sched_pelt_multiplier, " 4 8ms PELT HALIFE - roughly 50ms to go from 0 to max performance point.");
> +
> /*
> * Approximate the new util_avg value assuming an entity has continued to run
> * for @delta us.
> @@ -482,7 +530,7 @@ unsigned long approximate_util_avg(unsigned long util, u64 delta)
> if (unlikely(!delta))
> return util;
>
> - accumulate_sum(delta, &sa, 1, 0, 1);
> + accumulate_sum(delta << sched_pelt_lshift, &sa, 1, 0, 1);
> ___update_load_avg(&sa, 0);
>
> return sa.util_avg;
> @@ -494,7 +542,7 @@ unsigned long approximate_util_avg(unsigned long util, u64 delta)
> u64 approximate_runtime(unsigned long util)
> {
> struct sched_avg sa = {};
> - u64 delta = 1024; // period = 1024 = ~1ms
> + u64 delta = 1024 << sched_pelt_lshift; // period = 1024 = ~1ms
> u64 runtime = 0;
>
> if (unlikely(!util))
> diff --git a/kernel/sched/pelt.h b/kernel/sched/pelt.h
> index 3a0e0dc28721..9b35b5072bae 100644
> --- a/kernel/sched/pelt.h
> +++ b/kernel/sched/pelt.h
> @@ -61,6 +61,14 @@ static inline void cfs_se_util_change(struct sched_avg *avg)
> 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 rq *rq)
> /* 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 +129,27 @@ static inline void update_rq_clock_pelt(struct rq *rq, s64 delta)
> 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)
> +{
> + delta <<= READ_ONCE(sched_pelt_lshift);
> +
> + 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 +176,7 @@ static inline void update_idle_rq_clock_pelt(struct rq *rq)
> * 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 +247,18 @@ update_irq_load_avg(struct rq *rq, u64 running)
> 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) { }
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index bbece0eb053a..a7c89c623250 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -1029,6 +1029,7 @@ 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;
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