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;
Date:   Mon, 21 Nov 2022 19:50:42 +0100
From:   Michal =?iso-8859-1?Q?Koutn=FD?= <mkoutny@suse.com>
To:     Waiman Long <longman@redhat.com>
Cc:     Tejun Heo <tj@kernel.org>, Zefan Li <lizefan.x@bytedance.com>,
        Johannes Weiner <hannes@cmpxchg.org>, cgroups@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Subject: Re: [PATCH 2/2] cgroup/cpuset: Optimize cpuset_attach() on v2
Message-ID: <20221121185042.GA15225@blackbody.suse.cz>
References: <20221112221939.1272764-1-longman@redhat.com>
 <20221112221939.1272764-3-longman@redhat.com>
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha256;
        protocol="application/pgp-signature"; boundary="sm4nu43k4a2Rpi4c"
Content-Disposition: inline
In-Reply-To: <20221112221939.1272764-3-longman@redhat.com>
User-Agent: Mutt/1.10.1 (2018-07-13)
Precedence: bulk


--sm4nu43k4a2Rpi4c
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline

On Sat, Nov 12, 2022 at 05:19:39PM -0500, Waiman Long <longman@redhat.com> wrote:
> +	/*
> +	 * In the default hierarchy, enabling cpuset in the child cgroups
> +	 * will trigger a number of cpuset_attach() calls with no change
> +	 * in effective cpus and mems. In that case, we can optimize out
> +	 * by skipping the task iteration and update.
> +	 */
> +	if (cgroup_subsys_on_dfl(cpuset_cgrp_subsys) &&
> +	    !cpus_updated && !mems_updated) {

I'm just wondering -- why is this limited to the default hierarchy only?
IOW why can't v1 skip too (when favorable constness between cpusets).

Thanks,
Michal

--sm4nu43k4a2Rpi4c
Content-Type: application/pgp-signature; name="signature.asc"
Content-Description: Digital signature

-----BEGIN PGP SIGNATURE-----

iHUEARYIAB0WIQTrXXag4J0QvXXBmkMkDQmsBEOquQUCY3vIfwAKCRAkDQmsBEOq
ueSvAQCyC6t+4Kgc9Ku5M0Twd+wYTQLyFcMCodNhZGs2DG56GQEA96Cg26FgHBCF
4fx2Ow2jpg02roncB1d72afOmf7dwwc=
=Py+0
-----END PGP SIGNATURE-----

--sm4nu43k4a2Rpi4c--