Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Tue, 15 Nov 2022 13:55:31 +0100
From:   Alexander Gordeev <agordeev@linux.ibm.com>
To:     John Stultz <jstultz@google.com>
Cc:     Joel Fernandes <joel@joelfernandes.org>,
        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
Message-ID: <Y3OMQ+1D+AHbP72+@li-4a3a4a4c-28e5-11b2-a85c-a8d192c6f089.ibm.com>
References: <20221003232033.3404802-1-jstultz@google.com>
 <20221003232033.3404802-3-jstultz@google.com>
 <Y01NPB4sa8Z98ntK@li-4a3a4a4c-28e5-11b2-a85c-a8d192c6f089.ibm.com>
 <CANDhNCoTGNANDnOQ6touhreG_UEn1-N4T4BktWFxpLPSWVfrdA@mail.gmail.com>
 <Y0+/SAWUNRnhIW9b@li-4a3a4a4c-28e5-11b2-a85c-a8d192c6f089.ibm.com>
 <CANDhNCpQuQn_84yqErF2noAYDwdwNJQF-pr4JKVp1eZzH=+f9w@mail.gmail.com>
 <Y1FDegctcU2LrYGT@li-4a3a4a4c-28e5-11b2-a85c-a8d192c6f089.ibm.com>
 <Y1Q3vYjlFt/Imu5w@google.com>
 <Y1TxCTq5gxh4fIEd@li-4a3a4a4c-28e5-11b2-a85c-a8d192c6f089.ibm.com>
 <CANDhNCreB=Bm-X7WFp-oUtfR9uNRD=Vx8TehJ59HvF4Ke48ehQ@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CANDhNCreB=Bm-X7WFp-oUtfR9uNRD=Vx8TehJ59HvF4Ke48ehQ@mail.gmail.com>
Precedence: bulk

On Mon, Nov 14, 2022 at 11:08:36PM -0800, John Stultz wrote:

Hi John,
...
> > Right. So the check to deem a remote CPU unfit would (logically) look like this:
> >
> > (active | pending | ksoftirqd) & LONG_SOFTIRQ_MASK
...
> As run_ksoftirqd() basically looks at the pending set and calls
> __do_softirq() which then moves the bits from the pending mask  to
> active mask while they are being run.
> 
> So (pending|active)&LONG_SOFTIRQ_MASK seems like it should be a
> sufficient check regardless of if the remote cpu is in softirq or
> ksoftirqd, no?

I did not realize run_ksoftirqd()->__do_softirq() covers it.
Sorry for the noise.

Thanks!

> thanks
> -john