Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:7 as permitted sender) client-ip=2620:137:e000::3:7;
Date:   Wed, 27 Sep 2023 15:53:33 +0800
From:   Aaron Lu <aaron.lu@intel.com>
To:     Chen Yu <yu.c.chen@intel.com>
CC:     Peter Zijlstra <peterz@infradead.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Ingo Molnar <mingo@redhat.com>,
        "Vincent Guittot" <vincent.guittot@linaro.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        "Tim Chen" <tim.c.chen@intel.com>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ben Segall <bsegall@google.com>,
        "Mel Gorman" <mgorman@suse.de>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Valentin Schneider <vschneid@redhat.com>,
        K Prateek Nayak <kprateek.nayak@amd.com>,
        "Gautham R . Shenoy" <gautham.shenoy@amd.com>,
        <linux-kernel@vger.kernel.org>, Chen Yu <yu.chen.surf@gmail.com>
Subject: Re: [PATCH 1/2] sched/fair: Record the short sleeping time of a task
Message-ID: <20230927075333.GA210077@ziqianlu-dell>
References: <cover.1695704179.git.yu.c.chen@intel.com>
 <b17a3db703494bdae8492843f7303c13b0dbd0fc.1695704179.git.yu.c.chen@intel.com>
Content-Type: text/plain; charset="us-ascii"
Content-Disposition: inline
In-Reply-To: <b17a3db703494bdae8492843f7303c13b0dbd0fc.1695704179.git.yu.c.chen@intel.com>
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?XotLNL0gDIs5IQHr3CYFY1sY6DtNqql7fBYKcqQi5TUxmzYJpCHabCQNytWX?=
 =?us-ascii?Q?lO5fKV6vzjE96eQcraxK6Ro1WByxKNxZLwfYVrvR1MWZRhgnEb4Zef5U1Xgf?=
 =?us-ascii?Q?1pThTWS0Qd5KpbI9TtPGRsgnanZlt3LGKUIyB6G5u0j8ndBIXnEibJnEaIT0?=
 =?us-ascii?Q?g9FJVYouJkAF54yX3uS74EIm9Xiq9XbTAIhPS2JjZrwJvie3FB/liGcC5iAn?=
 =?us-ascii?Q?LHkDfq0+27ZvqIkyufxgp2qimT+eOfp98gUXGfDGMc5LX+naLL/93dhCjm2p?=
 =?us-ascii?Q?zEzx6/dSurxSiJf0zeIdcgDhG1D6lY7c1WHK2FZ1NpkMvK+kG4jcLIUQRyHy?=
 =?us-ascii?Q?bwG9pfcLECj/NhpRy/sb43jLq+QXShJhyP/SaoCCo6N2snmoX6zxvm51KT2j?=
 =?us-ascii?Q?gua5R7EkhSuVQZgKhcn8u0TjHru67zjqnwjBFPm6U5WtWsUqA4WfB7QPZqxj?=
 =?us-ascii?Q?YU4cK+RXfGbAruSTDQC1ijk8NLtIZOXkaZceIETI1BENNbF5rIGQf+5/vLVm?=
 =?us-ascii?Q?4OwYZwbYZdEdZ0VKLgKQYE0dtxKLB8Au3fDKwfxikOPTfU6LV+8xjwE5p0gy?=
 =?us-ascii?Q?QIV+/6lUPIDWm0YnG1LSSHBDof8n7x0Ld2gL/oxjWwN1Ub9GWve95Mk5yiev?=
 =?us-ascii?Q?SzH64A5QN2BDeo3YWFWPLmcxQWfPvTWQmnemyrQtYb62889YhjY1cYue1zkj?=
 =?us-ascii?Q?NtHnWIMEunt2dnP8l32IOxzB1uChqkY7SQ/eywirkr8N7+s9AUVhLfnmf0yB?=
 =?us-ascii?Q?HP/3quoEbhU2iutWcfmyfwG8nVZTOoJM5NbQRoURwwwChm4o2koFQh5RM2QH?=
 =?us-ascii?Q?LLQzC4sI6LkfH+KMXVcRxH6i6s2qYZqU6uKfttPdEJC0Sjk58B1POrmX/8Vz?=
 =?us-ascii?Q?C8c/s71W2bO44cHRO4XaR3Txbucb9dEZFMh9ldkRyRskcMq5uzYaEWDdS7JY?=
 =?us-ascii?Q?f1WG7n/yQ7RhhOf3gjT51pRLCKADbzRBvSqa8iJPy+hnqoEDXZAkKDPKxZHq?=
 =?us-ascii?Q?JJt5/3AUo70QUJmicVksIGuQl4g4UWjuZRwA0cy9aM/1Ie/Pws4gHbzqpfNe?=
 =?us-ascii?Q?pmtcAY1JRm2Fg/llCkKVBv3zYLFfU/+P0knoi07Ho2Fa1im7AATiF3IU0UK3?=
 =?us-ascii?Q?3iT/3hDyUlew4TeHqJXqOnRcwwWkr+UjunNMEdgSQ1B9hpVSdZa7gSi9K1tf?=
 =?us-ascii?Q?F+1m0Ck1DJ45MMti1+OuuyNLUQnfeytysoSwxI3JiTjBiIKJ1rOdJVMAqL4U?=
 =?us-ascii?Q?Z2pXmW9vGHSuSMCOQtvERVDURE46vuA/eGO5cKCn2mDVHmNtrC0sLI+CuTlr?=
 =?us-ascii?Q?NVTcJ//WkmUgNyOW5JKQGiSUkts0Ejzs58lC4fBBAgXhIsSHdTb39LukuUY5?=
 =?us-ascii?Q?25CqnxbYuqzGuRKzbeNad1kJoCYay0VhFF0F9Sg20+2LrI4WgYBV6ZAf59XJ?=
 =?us-ascii?Q?YC1uJncxqG+NPtHlJCW9rhyaoKBOeHMA08uiLTzH7UlS2t59tgG3dgsf2ruA?=
 =?us-ascii?Q?XC7fiNqx98shwB4lQBcU5pWkrlComONOBZdJdsl37ts70k/Di6lZrSoyw88o?=
 =?us-ascii?Q?fOLBfjgQzjAubBDN/M485X+PXdTgrT+o67lCcTmr?=
X-MS-Exchange-CrossTenant-Network-Message-Id: 8653f3cf-4db6-41d2-28cb-08dbbf2edff8
X-MS-Exchange-CrossTenant-AuthSource: BYAPR11MB3062.namprd11.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 27 Sep 2023 07:53:45.1281
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 46c98d88-e344-4ed4-8496-4ed7712e255d
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: J6SY1cuSQgjN1EAzyWxG+pjvEScB1Nw/Gta3NCF087EyET9SLEYttpuRYBdj+xtTvpw/jLlLB2FzomhygOcQDQ==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS7PR11MB7908
X-OriginatorOrg: intel.com
X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,
        DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,
        RCVD_IN_DNSWL_BLOCKED,RCVD_IN_MSPIKE_H3,RCVD_IN_MSPIKE_WL,
        SPF_HELO_NONE,SPF_NONE autolearn=ham autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
        lindbergh.monkeyblade.net
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
X-Greylist: Sender passed SPF test, not delayed by milter-greylist-4.6.4 (snail.vger.email [0.0.0.0]); Wed, 27 Sep 2023 00:54:03 -0700 (PDT)

On Tue, Sep 26, 2023 at 01:11:02PM +0800, Chen Yu wrote:
> During task wakeup, the wakee firstly checks if its previous
> running CPU is idle. If yes, choose that CPU as its first
> choice. However, in most cases, the wakee's previous CPU
> could be chosen by someone else, which breaks the cache
> locality.
> 
> Proposes a mechanism to reserve the task's previous
> CPU for a short while. In this reservation period, other
> tasks are not allowed to pick that CPU until a timeout.
> The reservation period is defined as the average short
> sleep time of the task. To be more specific, it is the
> time delta between this task being dequeued and enqueued.
> Only the sleep time shorter than sysctl_sched_migration_cost
> will be recorded. If the sleep time is longer than
> sysctl_sched_migration_cost, give the reservation period
> a penalty by shrinking it to half. In this way, the 'burst'
> sleeping time of the task is honored, meanwhile, if that
> task becomes a long-sleeper, the reservation time of that
> task is shrunk to reduce the impact on task wakeup.
> 
> Suggested-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> Signed-off-by: Chen Yu <yu.c.chen@intel.com>
> ---
>  include/linux/sched.h |  3 +++
>  kernel/sched/fair.c   | 21 +++++++++++++++++++++
>  2 files changed, 24 insertions(+)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index dc37ae787e33..4a0ac0276384 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -561,6 +561,9 @@ struct sched_entity {
>  	u64				vruntime;
>  	s64				vlag;
>  	u64				slice;
> +	u64				prev_dequeue_time;
> +	/* the reservation period of this task during wakeup */
> +	u64				sis_rsv_avg;

Nit: these info are only relavant for task, not group so might be better
to move them to task_struct to save a little memory?

>  
>  	u64				nr_migrations;
>  
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index d0877878bcdb..297b9470829c 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -6456,6 +6456,24 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
>  	struct sched_entity *se = &p->se;
>  	int idle_h_nr_running = task_has_idle_policy(p);
>  	int task_new = !(flags & ENQUEUE_WAKEUP);
> +	u64 last_dequeue = p->se.prev_dequeue_time;
> +	u64 now = sched_clock_cpu(task_cpu(p));

I think cpu_of(rq) is more clear than task_cpu(p). Using task_cpu(p)
seems to suggest task_cpu(p) can be different from cpu_of(rq).

> +
> +	/*
> +	 * If the task is a short-sleepting task, there is no need
> +	 * to migrate it to other CPUs. Estimate the average short sleeping
> +	 * time of the wakee. This sleep time is used as a hint to reserve
> +	 * the dequeued task's previous CPU for a short while. During this
> +	 * reservation period, select_idle_cpu() prevents other wakees from
> +	 * choosing this CPU. This could bring a better cache locality.
> +	 */
> +	if ((flags & ENQUEUE_WAKEUP) && last_dequeue && cpu_online(task_cpu(p)) &&

Hmm...the cpu_online() check looks weird. If the cpu is offlined, no task
will be enqueued there, right?

Thanks,
Aaron

> +	    now > last_dequeue) {
> +		if (now - last_dequeue < sysctl_sched_migration_cost)
> +			update_avg(&p->se.sis_rsv_avg, now - last_dequeue);
> +		else
> +			p->se.sis_rsv_avg >>= 1;
> +	}
>  
>  	/*
>  	 * The code below (indirectly) updates schedutil which looks at
> @@ -6550,6 +6568,7 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags)
>  	int task_sleep = flags & DEQUEUE_SLEEP;
>  	int idle_h_nr_running = task_has_idle_policy(p);
>  	bool was_sched_idle = sched_idle_rq(rq);
> +	u64 now;
>  
>  	util_est_dequeue(&rq->cfs, p);
>  
> @@ -6611,6 +6630,8 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags)
>  dequeue_throttle:
>  	util_est_update(&rq->cfs, p, task_sleep);
>  	hrtick_update(rq);
> +	now = sched_clock_cpu(cpu_of(rq));
> +	p->se.prev_dequeue_time = task_sleep ? now : 0;
>  }
>  
>  #ifdef CONFIG_SMP
> -- 
> 2.25.1
>