linux-kernel - Re: [RFC][PATCH 1/5] sched/fair: Fix select_idle

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Message-ID: <20210108130110.cj3zqsnjdt5mg3uz@e107158-lin>
Date:   Fri, 8 Jan 2021 13:01:10 +0000
From:   Qais Yousef <qais.yousef@....com>
To:     Mel Gorman <mgorman@...hsingularity.net>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        "Li, Aubrey" <aubrey.li@...ux.intel.com>,
        vincent.guittot@...aro.org, linux-kernel@...r.kernel.org,
        mingo@...hat.com, juri.lelli@...hat.com,
        valentin.schneider@....com, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com,
        tim.c.chen@...ux.intel.com, benbjiang@...il.com
Subject: Re: [RFC][PATCH 1/5] sched/fair: Fix select_idle_cpu()s cost
 accounting

On 01/08/21 10:27, Mel Gorman wrote:
>  	for_each_cpu_wrap(cpu, cpus, target) {
> -		if (available_idle_cpu(cpu) || sched_idle_cpu(cpu))
> +		if (available_idle_cpu(cpu) || sched_idle_cpu(cpu)) {
> +			/* Adjust cost of a successful scan */
> +			loops <<= 2;
> +
>  			break;
> +		}
>  
> -		if (loops >= nr) {
> +		if (++loops >= nr) {
>  			cpu = -1;
>  			break;
>  		}
> -		loops++;

Random (out of the blue) comment.

Now this will increment loops before the comparison/break. ie: we're
effectively doing one iteration less IIRC. Should loops be initialized to
0 instead of 1?

Thanks

--
Qais Yousef