Re: [tip:tracing/hw-branch-tracing] tracing/hw-branch-tracing: convert bts-tracer mutex to a spinlock

[Ingo Molnar <mingo@elte.hu>]

* Metzger, Markus T <markus.t.metzger@intel.com> wrote:

> > static void trace_bts_prepare(struct trace_iterator *iter)
> > {
> >-	mutex_lock(&bts_tracer_mutex);
> >+	spin_lock(&bts_tracer_lock);
> >
> > 	on_each_cpu(trace_bts_cpu, iter->tr, 1);
> >
> >-	mutex_unlock(&bts_tracer_mutex);
> >+	spin_unlock(&bts_tracer_lock);
> > }
> 
> Whereas start/stop are relatively fast, the above operation is 
> rather expensive. Would it make sense to use 
> schedule_on_each_cpu() instead of on_each_cpu()?

it's perfectly fine to do that on_each_cpu() under the spinlock. 
schedule_on_each_cpu() would likely be more expensive - and for 
no good reason.

	Ingo