From: Dietmar Eggemann <dietmar.eggemann@arm.com>
To: Qais Yousef <qyousef@layalina.io>
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.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 0/7] sched: cpufreq: Remove magic margins
Date: Tue, 12 Sep 2023 19:18:23 +0200 [thread overview]
Message-ID: <356ec193-5c89-4f7e-5e43-d600dff68cf9@arm.com> (raw)
In-Reply-To: <20230908140757.haewcuwsumphcv7p@airbuntu>
On 08/09/2023 16:07, Qais Yousef wrote:
> On 09/08/23 09:40, Dietmar Eggemann wrote:
>> On 08/09/2023 02:17, Qais Yousef wrote:
>>> On 09/07/23 15:08, Peter Zijlstra wrote:
>>>> On Mon, Aug 28, 2023 at 12:31:56AM +0100, Qais Yousef wrote:
[...]
>>> And what was a high end A78 is a mid core today. So if you look at today's
>>> mobile world topology we really have a tiy+big+huge combination of cores. The
>>> bigs are called mids, but they're very capable. Fits capacity forces migration
>>> to the 'huge' cores too soon with that 80% margin. While the 80% might be too
>>> small for the tiny ones as some workloads really struggle there if they hang on
>>> for too long. It doesn't help that these systems ship with 4ms tick. Something
>>> more to consider changing I guess.
>>
>> If this is the problem then you could simply make the margin (headroom)
>> a function of cpu_capacity_orig?
>
> I don't see what you mean. instead of capacity_of() but keep the 80%?
>
> Again, I could be delusional and misunderstanding everything, but what I really
> see fits_capacity() is about is misfit detection. But a task is not really
> misfit until it actually has a util above the capacity of the CPU. Now due to
> implementation details there can be a delay between the task crossing this
> capacity and being able to move it. Which what I believe this headroom is
> trying to achieve.
>
> I think we can better define this by tying this headroom to the worst case
> scenario it takes to actually move this misfit task to the right CPU. If it can
> continue to run without being impacted with this delay and crossing the
> capacity of the CPU it is on, then we should not trigger misfit IMO.
Instead of:
fits_capacity(unsigned long util, unsigned long capacity)
return approximate_util_avg(util, TICK_USEC) < capacity;
just make 1280 in:
#define fits_capacity(cap, max) ((cap) * 1280 < (max) * 1024)
dependent on cpu's capacity_orig or the capacity diff to the next higher
capacity_orig.
Typical example today: {little-medium-big capacity_orig} = {128, 896, 1024}
896÷128 = 7
1024/896 = 1.14
to achieve higher margin on little and lower margin on medium.
[...]
next prev parent reply other threads:[~2023-09-12 17:18 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
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 [this message]
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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