From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8FCD532F75E; Mon, 20 Oct 2025 17:00:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760979604; cv=none; b=pGx7JwBNw00Q2OczdLe+xceI/2z4OxzUmjn/fW5oG4d9uyVlNLtC01rMlnQTTqQeBP8wIENZGYenOa9QbrGKdEMHXGA2a0ev1U5CtEdB2TMIEgauM/BcXmgAezu/0bg1pjIfHRudLcAajTjx9RLWfN6SdlpesuZ2vMoMmY27hAo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760979604; c=relaxed/simple; bh=g9I0U02/cUqENuDToUCyNj2Rm3pn6hIWjCEcA13CqVo=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Es/TgemCm8fqzXSoCzf/535DIMnfACrcHG++9bvda9zl2VJBe7BJ1EcUTYBYElnLRt5uGuhZeMuChPZ4mmrfnPYDMox1CtTNPVeJZ7mDTpXHClq+ERrAYQTWfzu5kN3KJRHnt0rw/afMfISmAvw7i7ArL7YfW6ZIi0k4QnFCG40= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=nFxrdVgV; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="nFxrdVgV" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 502C2C4CEF9; Mon, 20 Oct 2025 17:00:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1760979604; bh=g9I0U02/cUqENuDToUCyNj2Rm3pn6hIWjCEcA13CqVo=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=nFxrdVgV1OsUGGgz+RBNH/ULZ4O4F8o8C2BPnuYcTmMHfntNko2ojmLiWnsYkLfKS tE+rtIRVtq5iRmDUft0siOw4bCBqn0FCzKOJV73chnDKRlmObMAaalMmZJxBldrwth SZSSFL0AnsiSldjcy0rqA/lYUr6KlrGRTAJohYKX7Ed/X3TfU2391jgSMC4IvVBNmt LEmV/cXQNW1L8Un5uNmAvSSs+Az79ry3LQEQqTR7ET7XnqV8gDXyvgiOAS3dt5aHya 6j2QPn+loM5LRBVrB+cwsErkebDaZcH8HcJhpe6Zzizk0bQjxl135KKn/Z7oMqpTDL b6Cxm8cDKdy7w== Date: Mon, 20 Oct 2025 07:00:03 -1000 From: Tejun Heo To: Waiman Long Cc: Johannes Weiner , Michal =?iso-8859-1?Q?Koutn=FD?= , cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Chen Ridong Subject: Re: [PATCH 2/2] cgroup/cpuset: Change callback_lock to raw_spinlock_t Message-ID: References: <20251020023207.177809-1-longman@redhat.com> <20251020023207.177809-3-longman@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251020023207.177809-3-longman@redhat.com> On Sun, Oct 19, 2025 at 10:32:07PM -0400, Waiman Long wrote: > The callback_lock is acquired either to read a stable set of cpu > or node masks or to modify those masks when cpuset_mutex is also > acquired. Sometime, it may need to go up the cgroup hierarchy while > holding the lock to find the right set of masks to use. Assuming that > the depth of the cgroup hierarch is finite and typically small, the > lock hold time should be limited. > > As a result, it can be converted to raw_spinlock_t to reduce overhead > in a PREEMPT_RT setting without introducing excessive latency. > > Signed-off-by: Waiman Long Is this something that RT people would like? Why does the overhead of the lock matter? I think this patch requires more justifications. Thanks. -- tejun