Re: [PATCH 00/21] rcu/context-tracking: Merge RCU eqs-dynticks counter to context tracking v2

Frederic Weisbecker
2022-05-19T15:09:00Z

On Wed, May 18, 2022 at 05:33:02PM +0200, Nicolas Saenz Julienne wrote:
> On Tue, 2022-05-03 at 12:00 +0200, Frederic Weisbecker wrote:
> > This mixes up the RCU dynticks counter and the context tracking state
> > updates into a single atomic instruction. This may serve several
> > purposes:
> >
> > 1) Improve CPU isolation with deferring some disturbances until sensitive
> > userspace workload completes and goes to the kernel. This can take
> > several forms, for example smp_call_function_housekeeping() or
> > on_each_housekeeping_cpu() to enqueue and execute work on all
> > housekeeping CPUs. Then an atomic operation on ct->state can defer
> > the work on nohz_full CPUs until they run in kernel (or IPI them
> > if they are in kernel mode), see this proposal by Peter:
> > https://lore.kernel.org/all/20210929151723.162004989@infradead.org/#r
> >
> > 2) Unearth sysidle (https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git/commit/?h=sysidle.2017.05.11a&id=fe5ac724d81a3c7803e60c2232718f212f3f38d4)
> > This feature allowed to shutdown the tick on the last housekeeping
> > CPU once the rest of the system is fully idle. We needed some proper
> > fully ordered context tracking for that.
> >
> > Inspired by Peterz: https://lore.kernel.org/all/20210929151723.162004989@infradead.org
> >
> > Passed 100 hours of TREE01.
> >
> > ---
>
> For the whole series:
>
> Reviewed-by: Nicolas Saenz Julienne <nsaenzju@redhat.com>
> Tested-by: Nicolas Saenz Julienne <nsaenzju@redhat.com>

I hesitated to apply these but the series has changed a little, although
the fundamental bits remain.

I'll just wait for a confirmation from you on this v3.

Thanks!