Re: [RFC PATCH RT] rwsem: The return of multi-reader PI rwsems

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

On Thu, Apr 10, 2014 at 03:17:41PM -0400, Steven Rostedt wrote:
> On Thu, 10 Apr 2014 17:36:17 +0200
> Peter Zijlstra <peterz@infradead.org> wrote:
> 
> 
> > It defaults to the total number of CPUs in the system, given the default
> > setup (all CPUs in a single balance domain), this should result in all
> > CPUs working concurrently on the boosted read sides.
> 
> Unfortunately, it currently defaults to the number of possible CPUs in
> the system. I should probably move the default assignment to after SMP
> is setup. Currently it happens in early boot before all the CPUs are
> running. On boot up, the limit is set to NR_CPUS which should be much
> higher than what the system has, but shouldn't matter during boot. But
> after all the CPUs are up and running, it can lower it to online CPUs.

Another approach is to use nr_cpu_ids, which is the maximum number of
CPUs that the particular booting system could ever have.  I use this in
RCU to resize the data structures down from their NR_CPUS compile-time
hugeness.

							Thanx, Paul

> I think I'll go and make v3 of this patch.
> 
> -- Steve
>