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Date: Sun, 21 Jan 2024 00:10:59 +0000
From: Qais Yousef <qyousef@layalina.io>
To: Ingo Molnar <mingo@kernel.org>, Peter Zijlstra <peterz@infradead.org>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: linux-kernel@vger.kernel.org, Pierre Gondois <Pierre.Gondois@arm.com>
Subject: Re: [PATCH v4 0/2] sched: Don't trigger misfit if affinity is
 restricted
Message-ID: <20240121001059.yygptzy6jzmcbbhk@airbuntu>
References: <20240105222014.1025040-1-qyousef@layalina.io>
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In-Reply-To: <20240105222014.1025040-1-qyousef@layalina.io>

Hi Vincent

On 01/05/24 22:20, Qais Yousef wrote:
> Changes since v3:
> 
> 	* Update commit message of patch 2 to be less verbose
> 
> Changes since v2:
> 
> 	* Convert access of asym_cap_list to be rcu protected
> 	* Add new patch to sort the list in descending order
> 	* Move some declarations inside affinity check block
> 	* Remove now redundant check against max_cpu_capacity in check_misfit_status()
> 
> (thanks Pierre!)
> 
> Changes since v1:
> 
> 	* Use asym_cap_list (thanks Dietmar) to iterate instead of iterating
> 	  through every cpu which Vincent was concerned about.
> 	* Use uclamped util to compare with capacity instead of util_fits_cpu()
> 	  when iterating through capcities (Dietmar).
> 	* Update commit log with test results to better demonstrate the problem
> 
> v1 discussion: https://lore.kernel.org/lkml/20230820203429.568884-1-qyousef@layalina.io/
> v2 discussion: https://lore.kernel.org/lkml/20231212154056.626978-1-qyousef@layalina.io/
> v3 discussion: https://lore.kernel.org/lkml/20231231175218.510721-1-qyousef@layalina.io/
> 
> Food for thoughts:
> ------------------
> 
> Should misfit cause balance_interval to double? This patch will still be needed
> if the answer is yes to avoid unnecessary misfit-lb to trigger repeatedly
> anyway.
> 
> Should the doubling be made independent of tick value? As it stands 3 failures
> for TICK = 1ms will increase it to 8ms. But for 4ms tick this will become 32ms
> after 3 failures. Which I think is too high too soon.
> 
> Should the balance_interval be capped to something more reasonable? On systems
> that require fast response (interactive Desktop for example);
> a balance_interval of 64ms and above seem too high.

Does this series address your concerns about scalability now?

If you have thoughts on the above that'd be great to hear too.


Thanks

--
Qais Yousef