netdev - Re: [PATCH v4 2/4] sched/isolation: Extend nohz

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Date:   Fri, 23 Oct 2020 15:25:05 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Nitesh Narayan Lal <nitesh@...hat.com>
Cc:     linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        linux-pci@...r.kernel.org, intel-wired-lan@...ts.osuosl.org,
        frederic@...nel.org, mtosatti@...hat.com, sassmann@...hat.com,
        jesse.brandeburg@...el.com, lihong.yang@...el.com,
        helgaas@...nel.org, jeffrey.t.kirsher@...el.com,
        jacob.e.keller@...el.com, jlelli@...hat.com, hch@...radead.org,
        bhelgaas@...gle.com, mike.marciniszyn@...el.com,
        dennis.dalessandro@...el.com, thomas.lendacky@....com,
        jiri@...dia.com, mingo@...hat.com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, lgoncalv@...hat.com,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v4 2/4] sched/isolation: Extend nohz_full to isolate
 managed IRQs

On Mon, Sep 28, 2020 at 02:35:27PM -0400, Nitesh Narayan Lal wrote:
> Extend nohz_full feature set to include isolation from managed IRQS. This

So you say it's for managed-irqs, the feature is actually called
MANAGED_IRQ, but, AFAICT, it does *NOT* in fact affect managed IRQs.

Also, as per Thomas' earlier points, managed-irqs are in fact perfectly
fine and don't need help at at...

> is required specifically for setups that only uses nohz_full and still
> requires isolation for maintaining lower latency for the listed CPUs.
> 
> Suggested-by: Frederic Weisbecker <frederic@...nel.org>
> Signed-off-by: Nitesh Narayan Lal <nitesh@...hat.com>
> ---
>  kernel/sched/isolation.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
> index 5a6ea03f9882..9df9598a9e39 100644
> --- a/kernel/sched/isolation.c
> +++ b/kernel/sched/isolation.c
> @@ -141,7 +141,7 @@ static int __init housekeeping_nohz_full_setup(char *str)
>  	unsigned int flags;
>  
>  	flags = HK_FLAG_TICK | HK_FLAG_WQ | HK_FLAG_TIMER | HK_FLAG_RCU |
> -		HK_FLAG_MISC | HK_FLAG_KTHREAD;
> +		HK_FLAG_MISC | HK_FLAG_KTHREAD | HK_FLAG_MANAGED_IRQ;
>  
>  	return housekeeping_setup(str, flags);
>  }
> -- 
> 2.18.2
>