> On Tue, Oct 4, 2022 at 7:41 AM Uladzislau Rezki <urezki@xxxxxxxxx> wrote:
> >
> > > trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("Check"));
> > > rcu_nocb_lock_irqsave(rdp, flags);
> > > lockdep_assert_held(&rdp->nocb_lock);
> > > bypass_ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
> > > - if (bypass_ncbs &&
> > > + lazy_ncbs = READ_ONCE(rdp->lazy_len);
> > > +
> > > + if (bypass_ncbs && (lazy_ncbs == bypass_ncbs) &&
> > > + (time_after(j, READ_ONCE(rdp->nocb_bypass_first) + jiffies_till_flush) ||
> > > + bypass_ncbs > 2 * qhimark)) {
> > Do you know why we want double "qhimark" threshold? It is not only this
> > place, there are several. I am asking because it is not expected by the
> > user.
>
> I am following the qhimark conventions in existing code. However
> qhimark does not mean that your callbacks cannot exceed these many or
> something, it is not a hard limit on queued callbacks.
>
> qhimark (And Paul can correct me) was introduced to reduce the number
> of callbacks after which RCU will not limit execution of callbacks to
> a batch of them. That has nothing to do with limiting the maximum
> number of callbacks, per-se. However, its usage certainly seems to
> have grown since that introduction.
>
> Maybe you are confusing it with blimit:
>
"blimit" controls how many/long callbacks are executed by the rcu_do_batch().
Whereas the "qhimark" controls when the bypass list is flushed to a regular one
to initiate gp and start executing.
--
Uladzislau Rezki
