From: Dietmar Eggemann <dietmar.eggemann@arm.com>
To: Qais Yousef <qyousef@layalina.io>
Cc: Ingo Molnar <mingo@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
"Rafael J. Wysocki" <rafael@kernel.org>,
Viresh Kumar <viresh.kumar@linaro.org>,
Vincent Guittot <vincent.guittot@linaro.org>,
linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
Lukasz Luba <lukasz.luba@arm.com>
Subject: Re: [RFC PATCH 1/7] sched/pelt: Add a new function to approximate the future util_avg value
Date: Wed, 13 Sep 2023 19:22:10 +0200 [thread overview]
Message-ID: <45548b21-280e-7f94-0b53-f2dcab6ccb5e@arm.com> (raw)
In-Reply-To: <20230910195832.pncjsqmkepichly6@airbuntu>
On 10/09/2023 21:58, Qais Yousef wrote:
> On 09/07/23 13:12, Dietmar Eggemann wrote:
>> On 06/09/2023 23:19, Qais Yousef wrote:
>>> On 09/06/23 14:56, Dietmar Eggemann wrote:
>>>> On 28/08/2023 01:31, Qais Yousef wrote:
[...]
>> Another thing ... I guess if you call accumulate_sum with delta the PELT
>> machinery assumes `delta = now - sa->last_update_time` which means you
>> would have to use `clock_pelt + TICK_USEC` as delta.
>
> Right.
>
> The way I understood it is that at TICK we should do update_load_avg() which
> would call __update_load_sum() which uses
>
> delta = now - sa->last_update_time
>
> which passes this delta to accumulate_sum()
>
> I can see we are not very accurate since there will be a small additional time
> besides TICK_USEC that we are not accounting for. But I can't see how this can
> cause a big error.
>
> predicted (assumed) tick time/delta
>
> sa->last_update_time = now
> tick_time = TICK_USEC + now
>
> delta = tick_time - sa->last_update_time
> delta = TICK_USEC + now - now
> delta = TICK_USEC
>
> but actual tick time/delta
>
> sa->last_update_time = now - x
> tick_time = TICK_USEC + now
>
> delta = tick_time - sa->last_update_time
> delta = TICK_USEC + now - (now - x)
> delta = TICK_USEC + x
>
> So the delta I am using might be slightly shorter than it should be.
>
> IIUC, what you're saying that the `x` in my equation above is clock_pelt,
> right?
No, I was wrong here. Calling accumulate_sum with `delta = TICK_USEC` is
fine.
accumulate_sum() will accrue `sa->util.sum` and ___update_load_avg()
will then adjust `sa->util_avg` accordingly.
delta should be 4000 on Arm64 boards so you will cross period
boundaries. In case `delta < 1024` you might want to not call
___update_load_avg() to be in pair with __update_load_avg_cfs_rq().
next prev parent reply other threads:[~2023-09-13 17:22 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 [this message]
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
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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