Date:   Thu, 2 Feb 2023 09:34:56 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Waiman Long <longman@redhat.com>
Cc:     Will Deacon <will@kernel.org>, linux-kernel@vger.kernel.org,
        kernel-team@android.com, Zefan Li <lizefan.x@bytedance.com>,
        Tejun Heo <tj@kernel.org>,
        Johannes Weiner <hannes@cmpxchg.org>, cgroups@vger.kernel.org
Subject: Re: [PATCH 1/2] cpuset: Fix cpuset_cpus_allowed() to not filter
 offline CPUs
Message-ID: <Y9t1sP/6nFht7RSN@hirez.programming.kicks-ass.net>
References: <20230131221719.3176-1-will@kernel.org>
 <20230131221719.3176-2-will@kernel.org>
 <6b068916-5e1b-a943-1aad-554964d8b746@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <6b068916-5e1b-a943-1aad-554964d8b746@redhat.com>
Precedence: bulk

On Tue, Jan 31, 2023 at 11:14:27PM -0500, Waiman Long wrote:

> A major concern I have is the overhead of creating a poor man version of v2
> cpus_allowed. This issue can be worked around even for cpuset v1 if it is
> mounted with the cpuset_v2_mode option to behave more like v2 in its cpumask
> handling. Alternatively we may be able to provide a config option to make
> this the default for v1 without the special mount option, if necessary.

It is equally broken for v2, it masks against effective_cpus. Not to
mention it explicitly starts with cpu_online_mask.