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Date: Sat, 10 Feb 2024 20:46:34 -0500
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Subject: Re: [RFC PATCH 0/8] cgroup/cpuset: Support RCU_NOCB on isolated
 partitions
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To: paulmck@kernel.org
Cc: Tejun Heo <tj@kernel.org>, Zefan Li <lizefan.x@bytedance.com>,
 Johannes Weiner <hannes@cmpxchg.org>,
 Frederic Weisbecker <frederic@kernel.org>, Jonathan Corbet <corbet@lwn.net>,
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 Alex Gladkov <agladkov@redhat.com>, Marcelo Tosatti <mtosatti@redhat.com>,
 Phil Auld <pauld@redhat.com>, Paul Gortmaker <paul.gortmaker@windriver.com>,
 Daniel Bristot de Oliveira <bristot@kernel.org>,
 Juri Lelli <juri.lelli@redhat.com>, Peter Zijlstra <peterz@infradead.org>,
 Costa Shulyupin <cshulyup@redhat.com>
References: <20240117163511.88173-1-longman@redhat.com>
 <ad806d7c-91ec-4659-9348-1b0bb42dd417@paulmck-laptop>
From: Waiman Long <longman@redhat.com>
In-Reply-To: <ad806d7c-91ec-4659-9348-1b0bb42dd417@paulmck-laptop>
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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