Re: [PATCH] tick/nohz: Narrow down noise while setting current task's tick dependency

[Frederic Weisbecker]

On Fri, May 15, 2020 at 08:07:18PM -0700, Paul E. McKenney wrote:
> On Fri, May 15, 2020 at 02:34:29AM +0200, Frederic Weisbecker wrote:
> > So far setting a tick dependency on any task, including current, used to
> > trigger an IPI to all CPUs. That's of course suboptimal but it wasn't
> > an issue as long as it was only used by posix-cpu-timers on nohz_full,
> > a combo that nobody seemed to use in real life.
> > 
> > But RCU started to use task tick dependency on current task to fix
> > stall issues on callbacks processing. These trigger regular and
> > undesired system wide IPIs on nohz_full.
> > 
> > The fix is very easy while setting a tick dependency on the current
> > task, only its CPU needs an IPI.
> 
> This passes moderate rcutorture testing.  If you want me to take it, please
> let me know, and otherwise:
> 
> Tested-by: Paul E. McKenney <paulmck@xxxxxxxxxx>

If you already have a pending urgent queue, I'd love you to take it.
If not I can take it.

Thanks.