Messages in this thread | | | Date | Tue, 4 Jul 2017 08:42:08 -0700 | From | Davidlohr Bueso <> | Subject | Re: [patch V2 2/2] mm/memory-hotplug: Switch locking to a percpu rwsem |
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On Tue, 04 Jul 2017, Thomas Gleixner wrote:
>On Tue, 4 Jul 2017, Davidlohr Bueso wrote: >> On Tue, 04 Jul 2017, Davidlohr Bueso wrote: >> >> > As a side effect you end up optimizing get/put_online_mems() at the cost >> > of more overhead for the actual hotplug operation, which is rare and of less >> > performance importance. >> >> So nm this, the reader side actually gets _more_ expensive with pcpu-rwsems >> due to at least two full barriers for each get/put operation. > >Compared to a mutex_lock/unlock() pair on a global mutex ....
Ah, right, I was thrown off the:
if (mem_hotplug.active_writer == current) return;
checks, which is only true within hotplug_begin/end. So normally we'd take the lock, which was my first impression. Sorry for the noise.
Thanks, Davidlohr
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