Re: [PATCH 0/4] Fix scalability problem in workqueue watchdog touch caused by stop_machine

[Nicholas Piggin]

On Wed Jun 26, 2024 at 12:53 AM AEST, Paul E. McKenney wrote:
> On Tue, Jun 25, 2024 at 09:42:43PM +1000, Nicholas Piggin wrote:
> > Here are a few patches to fix a lockup caused by very slow progress due
> > to a scalability problem in workqueue watchdog touch being hammered by
> > thousands of CPUs in multi_cpu_stop. Patch 2 is the fix.
> > 
> > I did notice when making a microbenchmark reproducer that the RCU call
> > was actually also causing slowdowns. Not nearly so bad as the workqueue
> > touch, but workqueue queueing of dummy jobs slowed down by a factor of
> > several times when lots of other CPUs were making
> > rcu_momentary_dyntick_idle() calls. So I did the stop_machine patches to
> > reduce that. So those patches 3,4 are independent of the first two and
> > can go in any order.
>
> For the series:
>
> Reviewed-by: Paul E. McKenney <paulmck@xxxxxxxxxx>

Oh, it did get a comment :) Thanks Paul. Not sure who owns the
multi_cpu_stop loop, Tejun and Peter I guess but that was 10+
years ago :P

I might ask Andrew if he would take patches 3-4, if there are
no objections.

Thanks,
Nick