Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [RFC v5 4/6] sched/fair: Tune task wake-up logic to pack small
 background tasks on fewer cores
To:     Hillf Danton <hdanton@sina.com>
Cc:     linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
        peterz@infradead.org, mingo@redhat.com, vincent.guittot@linaro.org,
        dietmar.eggemann@arm.com, patrick.bellasi@matbug.net,
        valentin.schneider@arm.com, pavel@ucw.cz, dsmythies@telus.net,
        Quentin Perret <qperret@qperret.net>,
        rafael.j.wysocki@intel.com, tim.c.chen@linux.intel.com,
        daniel.lezcano@linaro.org
References: <20191007083051.4820-1-parth@linux.ibm.com>
 <20191008132842.6612-1-hdanton@sina.com>
From:   Parth Shah <parth@linux.ibm.com>
Date:   Wed, 9 Oct 2019 14:52:54 +0530
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101
 Thunderbird/60.0
MIME-Version: 1.0
In-Reply-To: <20191008132842.6612-1-hdanton@sina.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Message-Id: <d4c936d9-c99f-e50d-95c9-0732ae45d1b9@linux.ibm.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


On 10/8/19 6:58 PM, Hillf Danton wrote:
> 
> On Mon,  7 Oct 2019 14:00:49 +0530 Parth Shah wrote:
>> +/*
>> + * Try to find a non idle core in the system  based on few heuristics:
>> + * - Keep track of overutilized (>80% util) and busy (>12.5% util) CPUs
>> + * - If none CPUs are busy then do not select the core for task packing
>> + * - If atleast one CPU is busy then do task packing unless overutilized CPUs
>> + *   count is < busy/2 CPU count
>> + * - Always select idle CPU for task packing
>> + */
>> +static int select_non_idle_core(struct task_struct *p, int prev_cpu, int target)
>> +{
>> +	struct cpumask *cpus = this_cpu_cpumask_var_ptr(turbo_sched_mask);
>> +	int iter_cpu, sibling;
>> +
>> +	cpumask_and(cpus, cpu_online_mask, p->cpus_ptr);
>> +
>> +	for_each_cpu_wrap(iter_cpu, cpus, prev_cpu) {
>> +		int idle_cpu_count = 0, non_idle_cpu_count = 0;
>> +		int overutil_cpu_count = 0;
>> +		int busy_cpu_count = 0;
>> +		int best_cpu = iter_cpu;
>> +
>> +		for_each_cpu(sibling, cpu_smt_mask(iter_cpu)) {
>> +			__cpumask_clear_cpu(sibling, cpus);
>> +			if (idle_cpu(iter_cpu)) {
> 
> Would you please elaborate the reasons that the iter cpu is checked idle
> more than once for finding a busy core?
> 

Thanks for looking at the patches.
Could you please point me out where iter_cpu is checked more than once?

>> +				idle_cpu_count++;
>> +				best_cpu = iter_cpu;
>> +			} else {
>> +				non_idle_cpu_count++;
>> +				if (cpu_overutilized(iter_cpu))
>> +					overutil_cpu_count++;
>> +				if (is_cpu_busy(cpu_util(iter_cpu)))
>> +					busy_cpu_count++;
>> +			}
>> +		}
>> +
>