Messages in this thread | | | Subject | Re: [PATCH 2/2] cpuhotplug: make get_online_cpus() scalability by using percpu counter | From | Peter Zijlstra <> | Date | Mon, 12 Apr 2010 11:28:59 +0200 |
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On Mon, 2010-04-12 at 17:24 +0800, Lai Jiangshan wrote: > Oleg Nesterov wrote: > > On 04/07, Oleg Nesterov wrote: > >> On 04/07, Lai Jiangshan wrote: > >>> Old get_online_cpus() is read-preference, I think the goal of this ability > >>> is allow get_online_cpus()/put_online_cpus() to be called nested. > >> Sure, I understand why you added task_struct->get_online_cpus_nest. > >> > >>> and use per-task counter for allowing get_online_cpus()/put_online_cpus() > >>> to be called nested, I think this deal is absolutely worth. > >> As I said, I am not going to argue. I can't justify this tradeoff. > > > > But, I must admit, I'd like to avoid adding the new member to task_struct. > > > > What do you think about the code below? > > > > I didn't even try to compile it, just to explain what I mean. > > > > In short: we have the per-cpu fast counters, plus the slow counter > > which is only used when cpu_hotplug_begin() is in progress. > > > > Oleg. > > > > get_online_cpus() in your code is still read-preference. > I wish we quit this ability of get_online_cpus().
Why?
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