linux-kernel - Re: [PATCH 2/3] sched/fair: Use HK_TYPE

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Message-ID: <e02862aa-7de5-4f16-845e-5ec7f1f41245@redhat.com>
Date: Fri, 6 Sep 2024 12:31:27 -0400
From: Waiman Long <longman@...hat.com>
To: Frederic Weisbecker <frederic@...nel.org>
Cc: Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
 Juri Lelli <juri.lelli@...hat.com>,
 Vincent Guittot <vincent.guittot@...aro.org>,
 Dietmar Eggemann <dietmar.eggemann@....com>,
 Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>,
 Mel Gorman <mgorman@...e.de>, Valentin Schneider <vschneid@...hat.com>,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] sched/fair: Use HK_TYPE_SCHED housekeeping CPUs

On 9/6/24 08:53, Frederic Weisbecker wrote:
> Le Wed, Sep 04, 2024 at 10:54:15AM -0400, Waiman Long a écrit :
>> On 9/3/24 09:53, Waiman Long wrote:
>>> On 9/3/24 09:12, Frederic Weisbecker wrote:
>>>> Le Sun, Aug 18, 2024 at 07:45:19PM -0400, Waiman Long a écrit :
>>>>> As the previous commit has enabled the setting of HK_TYPE_SCHED
>>>>> housekeeping CPUs in nohz_full setup, we can now use the more aptly
>>>>> named HK_TYPE_SCHED housekeeping CPUs instead of HK_TYPE_MISC.
>>>>>
>>>>> Signed-off-by: Waiman Long <longman@...hat.com>
>>>> Can we instead merge HK_FLAG_TICK, HK_FLAG_WQ, HK_FLAG_TIMER,
>>>> HK_FLAG_RCU,
>>>> HK_FLAG_MISC and HK_FLAG_KTHREAD into a single
>>>> HK_FLAG_KERNEL_NOISE / HK_TYPE_KERNEL_NOISE ?
>>> Sure. I am open to new name as I am not good on that.
>>> HK_FLAG_KERNEL_NOISE does make sense.
>> I can't merge HK_FLAG_TICK just yet as it can be independently set by using
>> isolcpus which can set just HK_TYPE_TICK, HK_TYPE_DOMAIN or
>> HK_TYPE_MANAGED_IRQ. That is the reason why they are still separate.
> Ah I think we really need to unify behaviours of isolcpus=nohz and nohz_full=
>
> diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
> index 5891e715f00d..9bc8fbf326cc 100644
> --- a/kernel/sched/isolation.c
> +++ b/kernel/sched/isolation.c
> @@ -212,7 +212,8 @@ static int __init housekeeping_isolcpus_setup(char *str)
>   	while (isalpha(*str)) {
>   		if (!strncmp(str, "nohz,", 5)) {
>   			str += 5;
> -			flags |= HK_FLAG_TICK;
> +			flags |= HK_FLAG_TICK | HK_FLAG_WQ | HK_FLAG_TIMER | HK_FLAG_RCU |
> +				 HK_FLAG_MISC | HK_FLAG_KTHREAD;
>   			continue;
>   		}

I am not against it, but it is a change in userspace behavior. How about 
we introduce "isolcpus=nohz_full" option that essentially combines 
isolcpus and nohz_full in one option? That can be a separate patch.

Cheers,
Longman