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SubjectRe: [PATCH v3 10/11] perf/x86/intel: Perform rotation on Intel CQM RMIDs
On Fri, 07 Nov, at 01:34:31PM, Peter Zijlstra wrote:
> On Thu, Nov 06, 2014 at 12:23:21PM +0000, Matt Fleming wrote:
> > + min_queue_time = entry->queue_time +
> > + msecs_to_jiffies(__rotation_period);
> > +
> > + if (time_after(min_queue_time, now))
> > + continue;
>
> Why continue; this LRU is time ordered, later entries cannot be earlier,
> right?

Good point. We can just exit here.

> > + set_bit(entry->rmid, cqm_limbo_bitmap);
> > + set_bit(entry->rmid, cqm_free_bitmap);
> > + }
> > +
> > + /*
> > + * Fast return if none of the RMIDs on the limbo list have been
> > + * sitting on the queue for the minimum queue time.
> > + */
> > + *available = !bitmap_empty(cqm_limbo_bitmap, nr_bits);
> > + if (!*available)
> > + return false;
> > +
> > + /*
> > + * Test whether an RMID is free for each package.
> > + */
> > + preempt_disable();
> > + smp_call_function_many(&cqm_cpumask, intel_cqm_stable, NULL, true);
> > + preempt_enable();
>
> I don't get the whole list -> bitmap -> list juggle.
>
> enum rmid_cycle_state {
> RMID_AVAILABLE = 0,
> RMID_LIMBO,
> RMID_YOUNG,
> };
>
> struct cqm_rmid_entry {
> ...
> enum rmid_cycle_state state;
> };
>
> static void __intel_sqm_stable(void *arg)
> {
> list_for_each_entry(entry, &cqm_rmid_limbo_lru, list) {
> if (entry->state == RMID_YOUNG)
> break;
>
> if (__rmid_read(entry->rmid) > __threshold)
> entry->state = RMID_LIMBO;
> }
> }
>
> static bool intel_cqm_rmid_stabilize()
> {
> unsigned long queue_time = jiffies + msecs_to_jiffies(__rotation_period);
> unsigned int nr_limbo = 0;
> ...
>
> list_for_each_entry(entry, &cqm_rmid_limbo_lru, list) {
> if (time_after(entry->queue_time, queue_time))
> break;
>
> entry->state = RMID_AVAILABLE;
> nr_limbo++;
> }
>
> if (!nr_limbo)
> return;
>
> on_each_cpu_mask(&cqm_cpumask, __intel_cqm_stable, NULL, true);
>
> list_for_each_entry_safe(entry, tmp, &cqm_rmid_limbo_lru, list) {
> if (entry->state == RMID_YOUNG)
> break;
>
> if (entry->state == RMID_AVAILABLE)
> list_move(&cqm_rmid_free_list, &entry->list);
> }
> }
>
>
> Would not something like that work?

Actually, yeah, that does look like it'd work. Are you OK with me adding
an enum to the cqm_rmid_entry? You had concerns in the past about
growing the size of the struct.

--
Matt Fleming, Intel Open Source Technology Center


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