Received-SPF: pass (google.com: domain of linux-kernel+bounces-214292-linux.lists.archive=gmail.com@vger.kernel.org designates 139.178.88.99 as permitted sender) client-ip=139.178.88.99;
Received-SPF: Pass (protection.outlook.com: domain of amd.com designates
 165.204.84.17 as permitted sender) receiver=protection.outlook.com;
 client-ip=165.204.84.17; helo=SATLEXMB04.amd.com; pr=C
Message-ID: <9d83771f-3d12-25f0-c3f8-70dd7942e9ce@amd.com>
Date: Fri, 14 Jun 2024 08:41:58 +0530
Precedence: bulk
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101
 Thunderbird/91.6.1
Subject: Re: [PATCH v2] sched/fair: Reschedule the cfs_rq when current is
 ineligible
Content-Language: en-US
To: Chen Yu <yu.c.chen@intel.com>, Chunxin Zang <spring.cxz@gmail.com>
CC: Honglei Wang <jameshongleiwang@126.com>, <mingo@redhat.com>, Peter
 Zijlstra <peterz@infradead.org>, <juri.lelli@redhat.com>,
	<vincent.guittot@linaro.org>, <dietmar.eggemann@arm.com>,
	<rostedt@goodmis.org>, <bsegall@google.com>, <mgorman@suse.de>,
	<bristot@redhat.com>, <vschneid@redhat.com>, Mike Galbraith <efault@gmx.de>,
	<linux-kernel@vger.kernel.org>, <yangchen11@lixiang.com>, Jerry Zhou
	<zhouchunhua@lixiang.com>, Chunxin Zang <zangchunxin@lixiang.com>
References: <20240529141806.16029-1-spring.cxz@gmail.com>
 <ZmKVjmuC4kGrUH5V@chenyu5-mobl2>
 <2E6EB0D6-D913-4205-B7DD-35EF4FA25667@gmail.com>
 <Zmrd2hwqHB8RQjqB@chenyu5-mobl2>
 <112FECA8-5D21-406F-814C-ACBE63351CBB@gmail.com>
 <ZmryuDqw2fEhHNni@chenyu5-mobl2>
From: K Prateek Nayak <kprateek.nayak@amd.com>
In-Reply-To: <ZmryuDqw2fEhHNni@chenyu5-mobl2>
Content-Type: text/plain; charset="UTF-8"; format=flowed
Content-Transfer-Encoding: 7bit
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 14 Jun 2024 03:12:11.3133
 (UTC)
X-MS-Exchange-CrossTenant-Network-Message-Id: a7cf57f5-50b5-432e-a9e8-08dc8c1fc87d
X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d
X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[SATLEXMB04.amd.com]
X-MS-Exchange-CrossTenant-AuthSource:
	BL6PEPF0001AB4D.namprd04.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Anonymous
X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem
X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS0PR12MB7632

Hello Chenyu,

Sorry, I'm a bit late to the thread but ...

On 6/13/2024 6:53 PM, Chen Yu wrote:
> [..snip..]
>>>
>>> I wonder if we can only take care of the NO_RUN_TO_PARITY case? Something like this,
>>>
>>>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>>>> index 03be0d1330a6..5e49a15bbdd3 100644
>>>> --- a/kernel/sched/fair.c
>>>> +++ b/kernel/sched/fair.c
>>>> @@ -745,6 +745,21 @@ int entity_eligible(struct cfs_rq *cfs_rq, struct sched_entity *se)
>>>>         return vruntime_eligible(cfs_rq, se->vruntime);
>>>> }
>>>>
>>>> +static bool check_entity_need_preempt(struct cfs_rq *cfs_rq, struct sched_entity *se)
>>>> +{
>>> if (sched_feat(RUN_TO_PARITY) || cfs_rq->nr_running <= 1 ||
>>>      !entity_eligible(cfs_rq, se))
>>> return false;
>>>
>>> return true;
>>>
>>> Thoughts?
>>>
>>
>> This does indeed look better. In that case, do I need to make the changes this way and send
>> out a version 3?
> 
> If you mean the following changes, maybe we can continue the discussion here.
> This is just my 2 cents, not sure what others think of it. Anyway, I can launch some tests.
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 8a5b1ae0aa55..c0fdb25f0695 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -744,6 +744,15 @@ int entity_eligible(struct cfs_rq *cfs_rq, struct sched_entity *se)
>   	return vruntime_eligible(cfs_rq, se->vruntime);
>   }
>   
> +static bool check_curr_preempt(struct cfs_rq *cfs_rq, struct sched_entity *curr)
> +{
> +	if (sched_feat(RUN_TO_PARITY) || cfs_rq->nr_running <= 1 ||
> +	    !entity_eligible(cfs_rq, curr))

Shouldn't this return false if "entity_eligible(cfs_rq, curr)" returns 
true since curr is still vruntime eligible on cfs_rq?

Would it better to have check_curr_preempt() as follows:

	if (sched_feat(RUN_TO_PARITY) || cfs_rq->nr_running <= 1)
		return false;

	return entity_eligible(cfs_rq, curr);

which returns false if curr is ineligible and scheduler can go ahead and 
and call schedule to evaluate the next best step?

Please let me know if I'm missing something.

> +		return false;
> +
> +	return true;
> +}
> +
>   static u64 __update_min_vruntime(struct cfs_rq *cfs_rq, u64 vruntime)
>   {
>   	u64 min_vruntime = cfs_rq->min_vruntime;
> [..snip..]

-- 
Thanks and Regards,
Prateek