From mboxrd@z Thu Jan 1 00:00:00 1970 From: Li Zefan Subject: Re: [PATCH 09/10] cpuset: allow to keep tasks in empty cpusets Date: Sat, 20 Apr 2013 09:22:09 +0800 Message-ID: <5171EDC1.4070805@huawei.com> References: <517137A7.4020605@huawei.com> <517138A4.3070209@huawei.com> <20130419205821.GA15543@mtj.dyndns.org> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20130419205821.GA15543-9pTldWuhBndy/B6EtB590w@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" To: Tejun Heo Cc: LKML , Cgroups , Containers , Glauber Costa On 2013/4/20 4:58, Tejun Heo wrote: > Hello, > > On Fri, Apr 19, 2013 at 08:29:24PM +0800, Li Zefan wrote: >> +static void update_tasks_cpumask_hier(struct cpuset *root_cs, >> + bool update_root, struct ptr_heap *heap) >> +{ >> + struct cpuset *cp; >> + struct cgroup *pos_cgrp; >> + >> + if (update_root) >> + update_tasks_cpumask(root_cs, heap); >> + >> + rcu_read_lock(); >> + cpuset_for_each_descendant_pre(cp, pos_cgrp, root_cs) { >> + /* skip the whole subtree if @cp have some CPU */ >> + if (!cpumask_empty(cp->cpus_allowed)) { >> + pos_cgrp = cgroup_rightmost_descendant(pos_cgrp); >> + continue; >> + } >> + >> + update_tasks_cpumask(cp, heap); >> + } >> + rcu_read_unlock(); > > I don't think we can call update_tasks_cpumask() under > rcu_read_lock(). It calls into set_cpus_allowed_ptr() which may > block, so you'll probably have to punt it to a work item like how Oh, will fix. > migration is being done. Another approach would be converting cgroup > to use SRCU instead, which would lessen pain on other places too. The > only problem there would be that srcu_read_lock() is a bit more > expensive than rcu_read_lock(). I'm not sure whether that'd show up > in some hot path or not. Ideas? > I guess we can live with rcu_read_lock() for now, and see if we can change it to srcu when other significant changes are done in all cgroup controllers. (hierarchy support in blkcg, etc..)