RE: [PATCH V7 3/6] perf, x86: handle multiple records in PEBS buffer

Liang, Kan
2015-05-05T17:22:45Z

> On Tue, May 05, 2015 at 04:30:25PM +0000, Liang, Kan wrote:
> > > > + for (at = base; at < top; at += x86_pmu.pebs_record_size) {
> > > > struct pebs_record_nhm *p = at;
> > > >
> > > > for_each_set_bit(bit, (unsigned long *)&p->status,
> > > > x86_pmu.max_pebs_events) {
> > > > event = cpuc->events[bit];
> > > > WARN_ON_ONCE(!event);
> > > >
> > > > + if (event->attr.precise_ip)
> > > > + break;
> > > > + }
> > >
> > > Would it make sense to delay looking for the event until you've
> > > found there is a single bit set -- and already know which bit that is?
> > >
> >
> > Yes, I think we can test cpuc->pebs_enabled here.
> > It should be better than attr.precise_ip checking.
> >
> > - for (; at < top; at += x86_pmu.pebs_record_size) {
> > + for (at = base; at < top; at += x86_pmu.pebs_record_size) {
> > struct pebs_record_nhm *p = at;
> >
> > for_each_set_bit(bit, (unsigned long *)&p->status,
> > x86_pmu.max_pebs_events) {
> > - event = cpuc->events[bit];
> > - if (!test_bit(bit, cpuc->active_mask))
> > - continue;
> > -
> > - WARN_ON_ONCE(!event);
> >
> > - if (!event->attr.precise_ip)
> > - continue;
> > + if (test_bit(bit, cpuc->pebs_enabled))
> > + break;
> > + }
> >
>
> Can't we take that entire for_each_set_bit() loop out?
>
> It appears to me we effectively do that single test_bit() test you left in
> there already with the & cpuc->pebs_enabled later on.
>
>
Right, will use find_first_bit to replace.

+ for (at = base; at < top; at += x86_pmu.pebs_record_size) {
struct pebs_record_nhm *p = at;

- for_each_set_bit(bit, (unsigned long *)&p->status,
- x86_pmu.max_pebs_events) {
- event = cpuc->events[bit];
- if (!test_bit(bit, cpuc->active_mask))
- continue;
-
- WARN_ON_ONCE(!event);
-
- if (!event->attr.precise_ip)
- continue;
-
- if (__test_and_set_bit(bit, (unsigned long *)&status))
+ bit = find_first_bit((unsigned long *)&p->status,
+ x86_pmu.max_pebs_events);

Thanks,
Kan