Re: [PATCH RFC tip/core/rcu 09/16] rcu-tasks: Add an RCU-tasks rude variant

Joel Fernandes
2020-03-16T21:45:55Z

On Mon, Mar 16, 2020 at 5:32 PM Steven Rostedt <rostedt@goodmis.org> wrote:
>
> On Mon, 16 Mar 2020 13:32:41 -0700
> "Paul E. McKenney" <paulmck@kernel.org> wrote:
>
> > > Just curious, why is the "rude" version better than SRCU? Seems the
> > > schedule_on_each_cpu() would be much slower than SRCU especially if
> > > there are 1000s of CPUs involved. Is there any reason that is a better
> > > alternative?
> >
> > The rude version has much faster readers, and the story I hear is that
> > there are not expected to be all that many concurrent updaters.
> >
> > But to get more detail, why not ask Steven why he chose not to use SRCU?
> > (I know the story for the BPF guys, and it is because of SRCU's read-side
> > overhead.)
>
> Same for the function side (if not even more so). This would require adding
> a srcu_read_lock() to all functions that can be traced! That would be a huge
> kill in performance. Probably to the point no one would bother even using
> function tracer.

Point well taken! Thanks,

-Joel