On Tue, Jan 20, 2026 at 12:53:26AM +0100, Frederic Weisbecker wrote:
> Le Mon, Jan 19, 2026 at 06:12:22PM -0500, Joel Fernandes a écrit :
> > During callback overload (exceeding qhimark), the NOCB code attempts
> > opportunistic advancement via rcu_advance_cbs_nowake(). Analysis shows
> > this entire code path is dead:
> >
> > - 30 overload conditions triggered with 300,000 callback flood
> > - 0 advancements actually occurred
> > - 100% of time blocked because current GP not done
> >
> > The overload condition triggers when callbacks are coming in at a high
> > rate with GPs not completing as fast. But the advancement requires the
> > GP to be complete - a logical contradiction. Even if the GP did complete
> > in time, nocb_gp_wait() has to wake up anyway to do the advancement, so
> > it is pointless.
> >
> > Since the advancement is dead code, the entire overload handling block
> > serves no purpose. Remove it entirely.
> >
> > Suggested-by: Frederic Weisbecker <[email protected]>
> > Signed-off-by: Joel Fernandes <[email protected]>
>
> Reviewed-by: Frederic Weisbecker <[email protected]>
>
> Would be nice to have Paul's ack as well, in case we missed something subtle
> here.
Given that you are good with it, I will take a look. And test it. ;-)
> Also probably for upcoming merge window + 1, note that similar code with
> similar removal opportunity resides in rcu_nocb_try_bypass().
> And ->nocb_gp_adv_time could then be removed.
Further simplification sounds like a good thing! Just not too simple,
you understand! ;-)
Thanx, Paul
