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: [PATCH v4 08/10] sched/fair: Steal work from an overloaded CPU
 when CPU goes idle
To:     Steve Sistare <steven.sistare@oracle.com>, mingo@redhat.com,
        peterz@infradead.org
Cc:     subhra.mazumdar@oracle.com, dhaval.giani@oracle.com,
        daniel.m.jordan@oracle.com, pavel.tatashin@microsoft.com,
        matt@codeblueprint.co.uk, umgwanakikbuti@gmail.com,
        riel@redhat.com, jbacik@fb.com, juri.lelli@redhat.com,
        vincent.guittot@linaro.org, quentin.perret@arm.com,
        linux-kernel@vger.kernel.org
References: <1544131696-2888-1-git-send-email-steven.sistare@oracle.com>
 <1544131696-2888-9-git-send-email-steven.sistare@oracle.com>
From:   Valentin Schneider <valentin.schneider@arm.com>
Message-ID: <e4d5f90a-8780-dc43-412b-0ac97fb3d39f@arm.com>
Date:   Fri, 7 Dec 2018 20:21:28 +0000
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101
 Thunderbird/60.2.1
MIME-Version: 1.0
In-Reply-To: <1544131696-2888-9-git-send-email-steven.sistare@oracle.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-GB
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Hi Steve,

On 06/12/2018 21:28, Steve Sistare wrote:
[...]
> @@ -6778,20 +6791,22 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_
>  	update_misfit_status(NULL, rq);
>  
>  	/*
> -	 * We must set idle_stamp _before_ calling idle_balance(), such that we
> -	 * measure the duration of idle_balance() as idle time.
> +	 * We must set idle_stamp _before_ calling try_steal() or
> +	 * idle_balance(), such that we measure the duration as idle time.
>  	 */
>  	rq_idle_stamp_update(rq);
>  

idle_balance() has a

	/*
	 * Do not pull tasks towards !active CPUs...
	 */
	if (!cpu_active(this_cpu))
		return 0;

check which we probably want for stealing too, so we could hoist it up here
to cover both idle_balance() and try_steal().

>  	new_tasks = idle_balance(rq, rf);
> +	if (new_tasks == 0)
> +		new_tasks = try_steal(rq, rf);
>  
>  	if (new_tasks)
>  		rq_idle_stamp_clear(rq);
>  
>  	/*
> -	 * Because idle_balance() releases (and re-acquires) rq->lock, it is
> -	 * possible for any higher priority task to appear. In that case we
> -	 * must re-start the pick_next_entity() loop.
> +	 * Because try_steal() and idle_balance() release (and re-acquire)
> +	 * rq->lock, it is possible for any higher priority task to appear.
> +	 * In that case we must re-start the pick_next_entity() loop.
>  	 */
>  	if (new_tasks < 0)
>  		return RETRY_TASK;
[...]