Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752705AbdLESYb (ORCPT ); Tue, 5 Dec 2017 13:24:31 -0500 Received: from mail-wm0-f65.google.com ([74.125.82.65]:37661 "EHLO mail-wm0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752628AbdLESY3 (ORCPT ); Tue, 5 Dec 2017 13:24:29 -0500 X-Google-Smtp-Source: AGs4zMZWJ8BjJIv0LNa6I7h5KO1eRktEwMQUhZZXFwXyV/6CuR5mKWZLm1v1CAQ32Wy8XD7PwLj/YaSj3nbpjgvdqc8= MIME-Version: 1.0 Reply-To: mtk.manpages@gmail.com In-Reply-To: <20171205171357.GU2421075@devbig577.frc2.facebook.com> References: <20171204214710.GM2421075@devbig577.frc2.facebook.com> <8fa060d2-07c7-7306-3d93-781c919f24eb@gmail.com> <20171205160049.GT2421075@devbig577.frc2.facebook.com> <20171205171357.GU2421075@devbig577.frc2.facebook.com> From: "Michael Kerrisk (man-pages)" Date: Tue, 5 Dec 2017 19:24:08 +0100 Message-ID: Subject: Re: [PATCH cgroup/for-4.15-fixes] cgroup: add warning about RT not being supported on cgroup2 To: Tejun Heo Cc: lkml , Lennart Poettering Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2130 Lines: 59 Hello Tejun, On 5 December 2017 at 18:13, Tejun Heo wrote: > From: Tejun Heo > Date: Tue, 5 Dec 2017 09:10:17 -0800 > > We haven't yet figured out what to do with RT threads on cgroup2. > Document the limitation. > > Signed-off-by: Tejun Heo > Reported-by: "Michael Kerrisk (man-pages)" > --- > Documentation/cgroup-v2.txt | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/Documentation/cgroup-v2.txt b/Documentation/cgroup-v2.txt > index 779211f..55a28f4 100644 > --- a/Documentation/cgroup-v2.txt > +++ b/Documentation/cgroup-v2.txt > @@ -898,6 +898,10 @@ controller implements weight and absolute bandwidth limit models for > normal scheduling policy and absolute bandwidth allocation model for > realtime scheduling policy. > > +WARNING: cgroup2 doesn't yet support control of realtime processes and > +the cpu controller can only be enabled when all RT processes are in > +the root cgroup. > + The documentation file already carries this useful text: [[ During transition to v2, system management software might still automount the v1 cgroup filesystem and so hijack all controllers during boot, before manual intervention is possible. To make testing and experimenting easier, the kernel parameter cgroup_no_v1= allows disabling controllers in v1 and make them always available in v2. ]] In that spirit, it may be worth alerting the reader that "system management software" might already have put some RT processes in nonroot cgroups. Maybe something like this: [[ WARNING: cgroup2 doesn't yet support control of realtime processes and the cpu controller can only be enabled when all RT processes are in the root cgroup. Be aware that 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. ]] Thanks, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/