Re: [patch V2 2/2] mm/memory-hotplug: Switch locking to a percpu rwsem

[Thomas Gleixner]

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 ....