From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joel Fernandes Subject: Re: [PATCH RFC] cpuset: Make cpusets get restored on hotplug Date: Thu, 26 Mar 2020 15:44:48 -0400 Message-ID: <20200326194448.GA133524@google.com> References: <20200326191623.129285-1-joel@joelfernandes.org> <20200326192035.GO162390@mtj.duckdns.org> Mime-Version: 1.0 Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=joelfernandes.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=Vz8M+WY12BuCsCLe/S9A2YcP2dqH4GItbGgYzpSKVks=; b=Wvi8sFDy3Xelku+ev0Z+8Z88gUwLdh49TKjzgpvENdRnjLybfJv52p2eJGWj4Po7mX 9ZiDd3dnWbFl0RVSEDSIc7JcCinAuAswL3ehy/VJRT+S+Z294BqheymwNr9VaspjVkRw jDTamd/KQWz5bhF0xB8oGvoDFbXtqoH/LflMo= Content-Disposition: inline In-Reply-To: <20200326192035.GO162390@mtj.duckdns.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Tejun Heo Cc: linux-kernel@vger.kernel.org, Dmitry Shmidt , Amit Pundir , kernel-team@android.com, jsbarnes@google.com, sonnyrao@google.com, vpillai@digitalocean.com, peterz@infradead.org, Guenter Roeck , Waiman Long , Greg Kerr , cgroups@vger.kernel.org, Johannes Weiner , Li Zefan Hi Tejun, On Thu, Mar 26, 2020 at 03:20:35PM -0400, Tejun Heo wrote: > On Thu, Mar 26, 2020 at 03:16:23PM -0400, Joel Fernandes (Google) wrote: > > This deliberately changes the behavior of the per-cpuset > > cpus file to not be effected by hotplug. When a cpu is offlined, > > it will be removed from the cpuset/cpus file. When a cpu is onlined, > > if the cpuset originally requested that that cpu was part of the cpuset, > > that cpu will be restored to the cpuset. The cpus files still > > have to be hierachical, but the ranges no longer have to be out of > > the currently online cpus, just the physically present cpus. > > This is already the behavior on cgroup2 and I don't think we want to > introduce this big a behavior change to cgroup1 cpuset at this point. It is not really that big a change. Please go over the patch, we are not changing anything with how ->cpus_allowed works and interacts with the rest of the system and the scheduler. We have just introduced a new mask to keep track of which CPUs were requested without them being affected by hotplug. On CPU onlining, we restore the state of ->cpus_allowed as not be affected by hotplug. There's 3 companies that have this issue so that should tell you something. We don't want to carry this patch forever. Many people consider the hotplug behavior to be completely broken. thanks, - Joel