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Subject: Re: Modifying isolcpus, nohz_full, and rcu_nocb kernel parameters at
 runtime
From:   Gianfranco Dutka <gianfranco.dutka@arista.com>
In-Reply-To: <d46834f4-a490-4a4a-9e95-cca4a6316570@redhat.com>
Date:   Fri, 8 Dec 2023 09:21:11 -0500
Cc:     Tejun Heo <tj@kernel.org>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        linux-kernel@vger.kernel.org, vincent.guittot@linaro.com,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Valentin Schneider <vschneid@redhat.com>,
        "Pandruvada, Srinivas" <srinivas.pandruvada@intel.com>,
        Frederic Weisbecker <frederic@kernel.org>
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References: <76587DD3-2A77-41A3-9807-6AEE4398EBA6@arista.com>
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 <d46834f4-a490-4a4a-9e95-cca4a6316570@redhat.com>
To:     Waiman Long <longman@redhat.com>
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> The isolcpus, nohz_full and rcu_nocbs are boot-time kernel parameters. =
I am in the process of improving dynamic CPU isolation at runtime. Right =
now, we are able to do isolcpus=3Ddomain with the isolated cpuset =
partition functionality. Other aspects of CPU isolation are being looked =
at with the goal of reducing the gap of what one can do at boot time =
versus what can be done at run time. It will certain take time to reach =
that goal.
>=20
> Cheers,
> Longman

Thank you Waiman for the response. It would seem that getting similar =
functionality through cgroups/cpusets is the only option at the moment. =
Is it completely out of the question to possibly patch the kernel to =
modify these parameters at runtime? Or would that entail a significant =
change that might not be so trivial to accomplish? For instance, the =
solution wouldn=E2=80=99t be as simple as patching the kernel to make =
these writeable and then calling the same functions which run at =
boot-time when these parameters are originally written?=20

Thanks,
Gianfranco=