Dipankar Sarma wrote:
>
> +static void force_quiescent_state(struct rcu_data *rdp,
> + struct rcu_ctrlblk *rcp)
> +{
> + int cpu;
> + cpumask_t cpumask;
> + set_need_resched();
> + if (unlikely(rdp->qlen - rdp->last_rs_qlen > rsinterval)) {
> + rdp->last_rs_qlen = rdp->qlen;
> + /*
> + * Don't send IPI to itself. With irqs disabled,
> + * rdp->cpu is the current cpu.
> + */
> + cpumask = rcp->cpumask;
> + cpu_clear(rdp->cpu, cpumask);
> + for_each_cpu_mask(cpu, cpumask)
> + smp_send_reschedule(cpu);
> + }
> +}
> [ ... snip ... ]
>
> @@ -92,17 +128,13 @@ void fastcall call_rcu(struct rcu_head *
> rdp = &__get_cpu_var(rcu_data);
> *rdp->nxttail = head;
> rdp->nxttail = &head->next;
> -
> - if (unlikely(++rdp->count > 10000))
> - set_need_resched();
> -
> + if (unlikely(++rdp->qlen > qhimark)) {
> + rdp->blimit = INT_MAX;
> + force_quiescent_state(rdp, &rcu_ctrlblk);
> + }
When ->qlen exceeds qhimark for the first time we send reschedule IPI to
other CPUs and force_quiescent_state() records ->last_rs_qlen = ->qlen.
But we don't reset ->last_rs_qlen when ->qlen goes to 0, this means that
next time we need ++rdp->qlen > qhimark + rsinterval to force other CPUS
to pass quiescent state, no?
Also, it seems to me it's better to have 2 counters, one for length(->donelist)
and another for length(->curlist + ->nxtlist). I think we don't need
force_quiescent_state() when all rcu callbacks are placed in ->donelist,
we only need to increase rdp->blimit in this case.
Oleg.
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