On 12/12, Oleg Nesterov wrote:

On 12/12, Srivatsa S. Bhat wrote:

quoted

On 12/12/2012 10:47 PM, Oleg Nesterov wrote:

quoted

Why it needs to be per-cpu? It can be global and __read_mostly to avoid
the false-sharing. OK, perhaps to put reader_percpu_refcnt/writer_signal
into a single cacheline...

Even I realized this (that we could use a global) after posting out the
series.. But do you think that it would be better to retain the per-cpu
variant itself, due to the cache effects?

I don't really know, up to you. This was the question ;)

But perhaps there is another reason to make it per-cpu...

It seems we can avoid cpu_hotplug.active_writer == current check in
get/put.

take_cpu_down() can clear this_cpu(writer_signal) right after it takes
hotplug_rwlock for writing. It runs with irqs and preemption disabled,
nobody else will ever look at writer_signal on its CPU.

Oleg.