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Date:   Sat, 22 Oct 2022 18:34:37 +0000
From:   Joel Fernandes <joel@joelfernandes.org>
To:     Alexander Gordeev <agordeev@linux.ibm.com>
Cc:     John Stultz <jstultz@google.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Connor O'Brien <connoro@google.com>,
        John Dias <joaodias@google.com>, Rick Yiu <rickyiu@google.com>,
        John Kacur <jkacur@redhat.com>,
        Qais Yousef <qais.yousef@arm.com>,
        Chris Redpath <chris.redpath@arm.com>,
        Abhijeet Dharmapurikar <adharmap@quicinc.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Thomas Gleixner <tglx@linutronix.de>, kernel-team@android.com,
        "J . Avila" <elavila@google.com>
Subject: Re: [PATCH RFC v4 2/3] sched: Avoid placing RT threads on cores
 handling long softirqs
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On Thu, Oct 20, 2022 at 02:47:54PM +0200, Alexander Gordeev wrote:
> On Wed, Oct 19, 2022 at 03:09:15PM -0700, John Stultz wrote:
> 
> Hi John,
> 
> [...]
> 
> > So I'll go ahead and simplify the check to just the LONG_SOFTIRQ_MASK
> > & (active | pending softirqs) check. This should avoid the need to
> > pull the cpu_rq(cpu)->curr value and simplify things.
> 
> In my reading of your approach if you find a way to additionally
> indicate long softirqs being handled by the remote ksoftirqd, it
> would cover all obvious/not-corner cases.

How will that help? The long softirq executing inside ksoftirqd will disable
preemption and prevent any RT task from executing.

Did I miss something?

thanks,

 - Joel