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Date:   Fri, 8 Jan 2021 13:01:10 +0000
From:   Qais Yousef <qais.yousef@arm.com>
To:     Mel Gorman <mgorman@techsingularity.net>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        "Li, Aubrey" <aubrey.li@linux.intel.com>,
        vincent.guittot@linaro.org, linux-kernel@vger.kernel.org,
        mingo@redhat.com, juri.lelli@redhat.com,
        valentin.schneider@arm.com, dietmar.eggemann@arm.com,
        rostedt@goodmis.org, bsegall@google.com,
        tim.c.chen@linux.intel.com, benbjiang@gmail.com
Subject: Re: [RFC][PATCH 1/5] sched/fair: Fix select_idle_cpu()s cost
 accounting
Message-ID: <20210108130110.cj3zqsnjdt5mg3uz@e107158-lin>
References: <20201214164822.402812729@infradead.org>
 <20201214170017.877557652@infradead.org>
 <c4e31235-e1fb-52ac-99a8-ae943ee0de54@linux.intel.com>
 <20201215075911.GA3040@hirez.programming.kicks-ass.net>
 <20210108102738.GB3592@techsingularity.net>
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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