From mboxrd@z Thu Jan 1 00:00:00 1970 From: Frederic Weisbecker Subject: Re: [PATCH v3 6/9] cgroup/cpuset: Add a new isolated cpus.partition type Date: Thu, 29 Jul 2021 13:03:31 +0200 Message-ID: <20210729110331.GC301667@lothringen> References: <20210720141834.10624-1-longman@redhat.com> <20210720141834.10624-7-longman@redhat.com> <20210727114241.GA283787@lothringen> Mime-Version: 1.0 Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1627556614; bh=uCbW9J3YqEIQSJj9wEXdcOHPabjCeLFizZzIoZQFBfg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=SKygjhxSpGxVYxPyQT8pgYAj5pGx1nIbzlIHdu7B9Trjb3QHSwOaL+8n6erSy1qE8 QwzIK8PqMKm8mB3l4dYF/xwSkYjM2S2gyiPRuFV1H4LTpxRfZ/dm4UtX7Sd0SmtuiW 0axwvVBceoswzdjQm9BCZ51E4X6sN9W5mWYFKTVbfZ8TXvUOLuESoyOLQSGqavi7j6 219KxzvEYwR+NGJLwraQsdv1Rs+E9hjAYXGAEldiDRBIxdWtGfqINqe0ibgR6BFCX4 7WeToS/NGh84MK9S0t8xV8QixU+1N2j/FYfVo2tUDsvBx3AalVLDlMxFbSB4uYslAz rLFvVKYv7AYpw== Content-Disposition: inline In-Reply-To: List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Waiman Long Cc: Tejun Heo , Zefan Li , Johannes Weiner , Jonathan Corbet , Shuah Khan , cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, Andrew Morton , Roman Gushchin , Phil Auld , Peter Zijlstra , Juri Lelli , Marcelo Tosatti , Michal =?iso-8859-1?Q?Koutn=FD?= On Tue, Jul 27, 2021 at 11:56:25AM -0400, Waiman Long wrote: > On 7/27/21 7:42 AM, Frederic Weisbecker wrote: > > On Tue, Jul 20, 2021 at 10:18:31AM -0400, Waiman Long wrote: > > > Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=TBD > > > > > > commit 994fb794cb252edd124a46ca0994e37a4726a100 > > > Author: Waiman Long > > > Date: Sat, 19 Jun 2021 13:28:19 -0400 > > > > > > cgroup/cpuset: Add a new isolated cpus.partition type > > > > > > Cpuset v1 uses the sched_load_balance control file to determine if load > > > balancing should be enabled. Cpuset v2 gets rid of sched_load_balance > > > as its use may require disabling load balancing at cgroup root. > > > > > > For workloads that require very low latency like DPDK, the latency > > > jitters caused by periodic load balancing may exceed the desired > > > latency limit. > > > > > > When cpuset v2 is in use, the only way to avoid this latency cost is to > > > use the "isolcpus=" kernel boot option to isolate a set of CPUs. After > > > the kernel boot, however, there is no way to add or remove CPUs from > > > this isolated set. For workloads that are more dynamic in nature, that > > > means users have to provision enough CPUs for the worst case situation > > > resulting in excess idle CPUs. > > > > > > To address this issue for cpuset v2, a new cpuset.cpus.partition type > > > "isolated" is added which allows the creation of a cpuset partition > > > without load balancing. This will allow system administrators to > > > dynamically adjust the size of isolated partition to the current need > > > of the workload without rebooting the system. > > > > > > Signed-off-by: Waiman Long > > > > > > Signed-off-by: Waiman Long > > Nice! And while we are adding a new ABI, can we take advantage of that and > > add a specific semantic that if a new isolated partition matches a subset of > > "isolcpus=", it automatically maps to it. This means that any further > > modification to that isolated partition will also modify the associated > > isolcpus= subset. > > > > Or to summarize, when we create a new isolated partition, remove the associated > > CPUs from isolcpus= ? > > We can certainly do that as a follow-on. I'm just concerned that this feature gets merged before we add that new isolcpus= implicit mapping, which technically is a new ABI. Well I guess I should hurry up and try to propose a patchset quickly once I'm back from vacation :-) > Another idea that I have been > thinking about is to automatically generating a isolated partition under > root to match the given isolcpus parameter when the v2 filesystem is > mounted. That needs more experimentation and testing to verify that it can > work. I thought about that too, mounting an "isolcpus" subdirectory withing the top cpuset but I was worried it could break userspace that wouldn't expect that new thing to show up. Thanks.