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:
#define DEFAULT_RCU_QHIMARK 10000 // If this many pending, ignore blimit.
static long qhimark = DEFAULT_RCU_QHIMARK;
#define DEFAULT_RCU_QLOMARK 100 // Once only this many pending, use blimit.
static long qlowmark = DEFAULT_RCU_QLOMARK;
thanks,
- Joel
