From: Qais Yousef <qyousef@layalina.io>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>,
"Rafael J. Wysocki" <rafael@kernel.org>,
Viresh Kumar <viresh.kumar@linaro.org>,
Vincent Guittot <vincent.guittot@linaro.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
Lukasz Luba <lukasz.luba@arm.com>
Subject: Re: [RFC PATCH 5/7] sched/schedutil: Add a new tunable to dictate response time
Date: Sun, 10 Sep 2023 20:25:01 +0100 [thread overview]
Message-ID: <20230910192501.5gjytpiubiizu2uh@airbuntu> (raw)
In-Reply-To: <20230907114420.GC10955@noisy.programming.kicks-ass.net>
On 09/07/23 13:44, Peter Zijlstra wrote:
> On Mon, Aug 28, 2023 at 12:32:01AM +0100, Qais Yousef wrote:
> > +static inline unsigned long
> > +sugov_apply_response_time(struct sugov_policy *sg_policy, unsigned long util)
> > +{
> > + unsigned long mult;
> > +
> > + if (sg_policy->freq_response_time_ms == sg_policy->tunables->response_time_ms)
> > + return util;
> > +
> > + mult = sg_policy->freq_response_time_ms * SCHED_CAPACITY_SCALE;
> > + mult /= sg_policy->tunables->response_time_ms;
> > + mult *= util;
> > +
> > + return mult >> SCHED_CAPACITY_SHIFT;
> > +}
> > +
> > static bool sugov_should_update_freq(struct sugov_policy *sg_policy, u64 time)
> > {
> > s64 delta_ns;
> > @@ -143,6 +184,7 @@ static unsigned int get_next_freq(struct sugov_policy *sg_policy,
> > unsigned int freq = arch_scale_freq_invariant() ?
> > policy->cpuinfo.max_freq : policy->cur;
> >
> > + util = sugov_apply_response_time(sg_policy, util);
> > freq = map_util_freq(util, freq, max);
> >
> > if (freq == sg_policy->cached_raw_freq && !sg_policy->need_freq_update)
>
> Urgh, so instead of caching the multiplier you keep computing what is
> essentially a constant over and over and over and over again :/
>
> That is, compute the whole 'freq_response_time_ms * SCHED_CAPACITY_SCALE
> / response_time_ms' thing *once*, when that file is written to, and then
> reduce the whole thing to:
>
> return (freq_response_mult * util) >> SCHED_CAPACITY_SHIFT;
>
> No need for that special case, no need for divisions, just go.
Yes! I was too focused am I doing the right thing, I didn't stop to think this
is actually a constant and can be done once too. I will fix it if this knobs
ends up hanging around.
Thanks!
--
Qais Yousef
next prev parent reply other threads:[~2023-09-10 19:25 UTC|newest]
Thread overview: 64+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-08-27 23:31 [RFC PATCH 0/7] sched: cpufreq: Remove magic margins Qais Yousef
2023-08-27 23:31 ` [RFC PATCH 1/7] sched/pelt: Add a new function to approximate the future util_avg value Qais Yousef
2023-09-06 12:56 ` Dietmar Eggemann
2023-09-06 21:19 ` Qais Yousef
2023-09-07 11:12 ` Dietmar Eggemann
2023-09-10 19:58 ` Qais Yousef
2023-09-13 17:22 ` Dietmar Eggemann
2023-09-16 19:49 ` Qais Yousef
2023-09-16 19:52 ` Qais Yousef
2023-08-27 23:31 ` [RFC PATCH 2/7] sched/pelt: Add a new function to approximate runtime to reach given util Qais Yousef
2023-09-06 12:56 ` Dietmar Eggemann
2023-09-06 20:44 ` Dietmar Eggemann
2023-09-06 21:38 ` Qais Yousef
2023-09-15 9:15 ` Hongyan Xia
2023-09-16 19:56 ` Qais Yousef
2023-08-27 23:31 ` [RFC PATCH 3/7] sched/fair: Remove magic margin in fits_capacity() Qais Yousef
2023-09-06 14:38 ` Dietmar Eggemann
2023-09-06 21:45 ` Qais Yousef
2023-08-27 23:32 ` [RFC PATCH 4/7] sched: cpufreq: Remove magic 1.25 headroom from apply_dvfs_headroom() Qais Yousef
2023-09-07 11:34 ` Peter Zijlstra
2023-09-10 19:23 ` Qais Yousef
2023-08-27 23:32 ` [RFC PATCH 5/7] sched/schedutil: Add a new tunable to dictate response time Qais Yousef
2023-09-06 21:13 ` Dietmar Eggemann
2023-09-06 21:52 ` Qais Yousef
2023-09-07 11:44 ` Peter Zijlstra
2023-09-10 19:25 ` Qais Yousef [this message]
2023-08-27 23:32 ` [RFC PATCH 6/7] sched/pelt: Introduce PELT multiplier Qais Yousef
2023-08-27 23:32 ` [RFC PATCH 7/7] cpufreq: Change default transition delay to 2ms Qais Yousef
2023-09-06 9:18 ` [RFC PATCH 0/7] sched: cpufreq: Remove magic margins Lukasz Luba
2023-09-06 21:18 ` Qais Yousef
2023-09-07 7:48 ` Lukasz Luba
2023-09-07 11:53 ` Peter Zijlstra
2023-09-07 13:06 ` Lukasz Luba
2023-09-07 13:29 ` Peter Zijlstra
2023-09-07 13:33 ` Lukasz Luba
2023-09-07 13:38 ` Peter Zijlstra
2023-09-07 13:45 ` Lukasz Luba
2023-09-08 12:51 ` Daniel Bristot de Oliveira
2023-09-12 11:57 ` Lukasz Luba
2023-09-10 18:20 ` Qais Yousef
2023-09-10 18:14 ` Qais Yousef
2023-09-07 13:26 ` Peter Zijlstra
2023-09-07 13:57 ` Lukasz Luba
2023-09-07 14:29 ` Peter Zijlstra
2023-09-07 14:42 ` Lukasz Luba
2023-09-07 20:16 ` Peter Zijlstra
2023-09-12 11:51 ` Lukasz Luba
2023-09-12 14:01 ` Vincent Guittot
2023-09-13 9:53 ` Lukasz Luba
2023-09-12 14:28 ` Peter Zijlstra
2023-09-10 19:06 ` Qais Yousef
2023-09-10 18:46 ` Qais Yousef
2023-09-07 13:08 ` Peter Zijlstra
2023-09-08 0:17 ` Qais Yousef
2023-09-08 7:40 ` Dietmar Eggemann
2023-09-08 14:07 ` Qais Yousef
2023-09-12 17:18 ` Dietmar Eggemann
2023-09-16 19:38 ` Qais Yousef
2023-09-08 10:25 ` Peter Zijlstra
2023-09-08 13:33 ` Qais Yousef
2023-09-08 13:58 ` Peter Zijlstra
2023-09-08 13:59 ` Peter Zijlstra
2023-09-08 14:11 ` Qais Yousef
2023-09-10 21:17 ` Qais Yousef
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