linux-kernel - Re: [PATCH] sched/fair: Simplify continue

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Message-ID: <6c1eed8f-455f-4612-be4e-02876f35e37e@arm.com>
Date: Tue, 26 Mar 2024 16:11:31 +0100
From: Dietmar Eggemann <dietmar.eggemann@....com>
To: Shrikanth Hegde <sshegde@...ux.ibm.com>, Ingo Molnar <mingo@...nel.org>
Cc: peterz@...radead.org, vincent.guittot@...aro.org, qyousef@...alina.io,
 linux-kernel@...r.kernel.org, vschneid@...hat.com, joshdon@...gle.com,
 riel@...riel.com
Subject: Re: [PATCH] sched/fair: Simplify continue_balancing for newidle

On 26/03/2024 10:00, Shrikanth Hegde wrote:
> 
> On 3/26/24 1:37 PM, Ingo Molnar wrote:
>>
>> * Shrikanth Hegde <sshegde@...ux.ibm.com> wrote:
>>

[...]

>> Is this actually true? Any change to behavior invalidates such a sentence.
> 
> From what i think, code path is same and I don't see any functionality changing. 
> Correct me if i am wrong. 
> 
> Currently, sched_balance_newidle does the same check to bail out as the
> should_we_balance check in case of newidle.  i.e  
> 
> should_we_balance
> 	if (env->dst_rq->nr_running > 0 || env->dst_rq->ttwu_pending)
> 			return 0;
> 
> sched_balance_newidle
> 		if (pulled_task || this_rq->nr_running > 0 ||
> 			this_rq->ttwu_pending)
> 			break;
> 		}

LGTM. Commit 792b9f65a568 ("sched: Allow newidle balancing to bail out
of load_balance") (Jun 22) made sure that we leave sched_balance_rq()
(former load_balance()) for CPU_NEWLY_IDLE asap to reduce wakeup latency.

So IMHO, we can use 'continue_balancing' instead of 'this_rq->nr_running
> 0 || this_rq->ttwu_pending' in sched_balance_newidle() (former
newidle_balance()).

Reviewed-by: Dietmar Eggemann <dietmar.eggemann@....com>