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([2601:188:c100:5710:627d:9ff:fe85:9ade]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7c3bfb2a5e3sm392543585a.41.2025.03.05.06.13.51 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 05 Mar 2025 06:13:51 -0800 (PST) From: Waiman Long X-Google-Original-From: Waiman Long Message-ID: <6a6d4c61-a318-444f-b089-1776beb8873d@redhat.com> Date: Wed, 5 Mar 2025 09:13:50 -0500 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] cgroup, docs: Be explicit about independence of RT_GROUP_SCHED and non-cpu controllers To: shashank.mahadasyam@sony.com, Tejun Heo , Johannes Weiner , =?UTF-8?Q?Michal_Koutn=C3=BD?= , Jonathan Corbet Cc: cgroups@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, Shinya Takumi References: <20250305-rt-and-cpu-controller-doc-v1-0-7b6a6f5ff43d@sony.com> <20250305-rt-and-cpu-controller-doc-v1-1-7b6a6f5ff43d@sony.com> Content-Language: en-US In-Reply-To: <20250305-rt-and-cpu-controller-doc-v1-1-7b6a6f5ff43d@sony.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 3/4/25 11:12 PM, Shashank Balaji via B4 Relay wrote: > From: Shashank Balaji > > The cgroup v2 cpu controller has a limitation that if > CONFIG_RT_GROUP_SCHED is enabled, the cpu controller can be enabled only > if all the realtime processes are in the root cgroup. The other > controllers have no such restriction. They can be used for the resource > control of realtime processes irrespective of whether > CONFIG_RT_GROUP_SCHED is enabled or not. > > Signed-off-by: Shashank Balaji > --- > Documentation/admin-guide/cgroup-v2.rst | 23 ++++++++++++++--------- > 1 file changed, 14 insertions(+), 9 deletions(-) > > diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst > index cb1b4e759b7e267c24d7f4f69564c16fb29c4d89..f293a13b42ed69e7c6bf5e974cb86e228411af4e 100644 > --- a/Documentation/admin-guide/cgroup-v2.rst > +++ b/Documentation/admin-guide/cgroup-v2.rst > @@ -1076,15 +1076,20 @@ cpufreq governor about the minimum desired frequency which should always be > provided by a CPU, as well as the maximum desired frequency, which should not > be exceeded by a CPU. > > -WARNING: cgroup2 doesn't yet support control of realtime processes. For > -a kernel built with the CONFIG_RT_GROUP_SCHED option enabled for group > -scheduling of realtime processes, the cpu controller can only be enabled > -when all RT processes are in the root cgroup. This limitation does > -not apply if CONFIG_RT_GROUP_SCHED is disabled. Be aware that system > -management software may already have placed RT processes into nonroot > -cgroups during the system boot process, and these processes may need > -to be moved to the root cgroup before the cpu controller can be enabled > -with a CONFIG_RT_GROUP_SCHED enabled kernel. > +WARNING: cgroup2 cpu controller doesn't yet fully support the control of > +realtime processes. For a kernel built with the CONFIG_RT_GROUP_SCHED option > +enabled for group scheduling of realtime processes, the cpu controller can only > +be enabled when all RT processes are in the root cgroup. Be aware that system > +management software may already have placed RT processes into non-root cgroups > +during the system boot process, and these processes may need to be moved to the > +root cgroup before the cpu controller can be enabled with a > +CONFIG_RT_GROUP_SCHED enabled kernel. > + > +With CONFIG_RT_GROUP_SCHED disabled, this limitation does not apply and some of > +the interface files either affect realtime processes or account for them. See > +the following section for details. Only the cpu controller is affected by > +CONFIG_RT_GROUP_SCHED. Other controllers can be used for the resource control of > +realtime processes irrespective of CONFIG_RT_GROUP_SCHED. > > > CPU Interface Files LGTM Acked-by: Waiman Long