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;
Sender: Tejun Heo <htejun@gmail.com>
Date:   Tue, 6 Jun 2023 10:13:31 -1000
From:   Tejun Heo <tj@kernel.org>
To:     Waiman Long <longman@redhat.com>
Cc:     Michal =?iso-8859-1?Q?Koutn=FD?= <mkoutny@suse.com>,
        Zefan Li <lizefan.x@bytedance.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Shuah Khan <shuah@kernel.org>, linux-kernel@vger.kernel.org,
        cgroups@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-kselftest@vger.kernel.org,
        Juri Lelli <juri.lelli@redhat.com>,
        Valentin Schneider <vschneid@redhat.com>,
        Frederic Weisbecker <frederic@kernel.org>,
        Mrunal Patel <mpatel@redhat.com>,
        Ryan Phillips <rphillips@redhat.com>,
        Brent Rowsell <browsell@redhat.com>,
        Peter Hunt <pehunt@redhat.com>, Phil Auld <pauld@redhat.com>
Subject: Re: [RFC PATCH 0/5] cgroup/cpuset: A new "isolcpus" paritition
Message-ID: <ZH-Ta7jDozegNo3o@slm.duckdns.org>
References: <759603dd-7538-54ad-e63d-bb827b618ae3@redhat.com>
 <405b2805-538c-790b-5bf8-e90d3660f116@redhat.com>
 <ZGvHUjOCjwat91Gq@slm.duckdns.org>
 <18793f4a-fd39-2e71-0b77-856afb01547b@redhat.com>
 <ZH4jfmypOXGJPu0D@slm.duckdns.org>
 <be64a569-4388-9dd9-3e06-36d716a54f6c@redhat.com>
 <ZH5FNc6wjlGPsaaO@slm.duckdns.org>
 <a2220c9f-7a8d-da82-ecc0-b39f3807408c@redhat.com>
 <ZH-P7X_yjnVfhy7b@slm.duckdns.org>
 <563fd5e1-650a-e329-8aab-2fa1953a9f49@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <563fd5e1-650a-e329-8aab-2fa1953a9f49@redhat.com>
Precedence: bulk

Hello,

On Tue, Jun 06, 2023 at 04:11:02PM -0400, Waiman Long wrote:
...
> The current CPU exclusive behavior is limited to sibling cgroups only.
> Because of the hierarchical nature of cpu distribution, the set of exclusive
> CPUs have to appear in all its ancestors. When partition is enabled, we do a
> sibling exclusivity test at that point to verify that it is exclusive. It
> looks like you want to do an exclusivity test even when the partition isn't
> active. I can certainly do that when the file is being updated. However, it
> will fail the write if the exclusivity test fails just like the v1
> cpuset.cpus.exclusive flag if you are OK with that.

Yeah, doesn't look like there's a way around it if we want to make
.exclusive a feature which is useful on its own.

> > Instead, it can be sth like "if the parent is a
> > partition root, cpuset implicitly tries to set all CPUs in its cpus file in
> > its cpus.exclusive file" so that user-visible behavior stays unchanged
> > depending on past history.
> 
> If parent is a partition root, auto reservation will be done and
> cpus.exclusive will be set automatically just like before. So existing
> applications using partition will not be affected.

Sounds great.

Thanks.

-- 
tejun