linux-kernel - Re: [RFC PATCH 0/8] cgroup/cpuset: Support RCU

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Message-ID: <099a0310-6805-4ad5-aa99-2589e768acd6@redhat.com>
Date: Sat, 10 Feb 2024 20:46:34 -0500
From: Waiman Long <longman@...hat.com>
To: paulmck@...nel.org
Cc: Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
 Johannes Weiner <hannes@...xchg.org>,
 Frederic Weisbecker <frederic@...nel.org>, Jonathan Corbet <corbet@....net>,
 Neeraj Upadhyay <quic_neeraju@...cinc.com>,
 Joel Fernandes <joel@...lfernandes.org>,
 Josh Triplett <josh@...htriplett.org>, Boqun Feng <boqun.feng@...il.com>,
 Steven Rostedt <rostedt@...dmis.org>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Lai Jiangshan <jiangshanlai@...il.com>, Zqiang <qiang.zhang1211@...il.com>,
 Davidlohr Bueso <dave@...olabs.net>, Shuah Khan <shuah@...nel.org>,
 cgroups@...r.kernel.org, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, rcu@...r.kernel.org,
 linux-kselftest@...r.kernel.org, Mrunal Patel <mpatel@...hat.com>,
 Ryan Phillips <rphillips@...hat.com>, Brent Rowsell <browsell@...hat.com>,
 Peter Hunt <pehunt@...hat.com>, Cestmir Kalina <ckalina@...hat.com>,
 Nicolas Saenz Julienne <nsaenz@...nel.org>,
 Alex Gladkov <agladkov@...hat.com>, Marcelo Tosatti <mtosatti@...hat.com>,
 Phil Auld <pauld@...hat.com>, Paul Gortmaker <paul.gortmaker@...driver.com>,
 Daniel Bristot de Oliveira <bristot@...nel.org>,
 Juri Lelli <juri.lelli@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
 Costa Shulyupin <cshulyup@...hat.com>
Subject: Re: [RFC PATCH 0/8] cgroup/cpuset: Support RCU_NOCB on isolated
 partitions

On 1/19/24 05:24, Paul E. McKenney wrote:
> On Wed, Jan 17, 2024 at 11:35:03AM -0500, Waiman Long wrote:
>> This patch series is based on the RFC patch from Frederic [1]. Instead
>> of offering RCU_NOCB as a separate option, it is now lumped into a
>> root-only cpuset.cpus.isolation_full flag that will enable all the
>> additional CPU isolation capabilities available for isolated partitions
>> if set. RCU_NOCB is just the first one to this party. Additional dynamic
>> CPU isolation capabilities will be added in the future.
>>
>> The first 2 patches are adopted from Federic with minor twists to fix
>> merge conflicts and compilation issue. The rests are for implementing
>> the new cpuset.cpus.isolation_full interface which is essentially a flag
>> to globally enable or disable full CPU isolation on isolated partitions.
>> On read, it also shows the CPU isolation capabilities that are currently
>> enabled. RCU_NOCB requires that the rcu_nocbs option be present in
>> the kernel boot command line. Without that, the rcu_nocb functionality
>> cannot be enabled even if the isolation_full flag is set. So we allow
>> users to check the isolation_full file to verify that if the desired
>> CPU isolation capability is enabled or not.
>>
>> Only sanity checking has been done so far. More testing, especially on
>> the RCU side, will be needed.
> There has been some discussion of simplifying the (de-)offloading code
> to handle only offline CPUs.  Along with some discussion of eliminating
> the (de-)offloading capability altogehter.
>
> We clearly should converge on the capability to be provided before
> exposing this to userspace.  ;-)

Would you mind giving me a pointer to the discussion of simplifying the 
de-offloading code to  handle only offline CPUs?

Thanks,
Longman