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

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Date: Tue, 26 Mar 2024 20:15:55 +0100
From: Ingo Molnar <mingo@...nel.org>
To: Dietmar Eggemann <dietmar.eggemann@....com>
Cc: Shrikanth Hegde <sshegde@...ux.ibm.com>, 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


* Dietmar Eggemann <dietmar.eggemann@....com> wrote:

> 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>

Thanks for the clarification, applied!

	Ingo