linux-kernel - Re: [PATCH v2 1/4] perf-events: Add support for supplementary event registers

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Date:	Wed, 2 Mar 2011 08:48:19 +0100
From:	Stephane Eranian <eranian@...gle.com>
To:	Lin Ming <ming.m.lin@...el.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>, Andi Kleen <andi@...stfloor.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/4] perf-events: Add support for supplementary event registers

On Wed, Mar 2, 2011 at 1:37 AM, Lin Ming <ming.m.lin@...el.com> wrote:
> On Wed, 2011-03-02 at 01:09 +0800, Stephane Eranian wrote:
>> Lin,
>>
>> See comments below:
>>
>> On Tue, Mar 1, 2011 at 5:47 PM, Lin Ming <ming.m.lin@...el.com> wrote:
>> > From: Andi Kleen <ak@...ux.intel.com>
>> >  static struct event_constraint *
>> > +intel_percore_constraints(struct cpu_hw_events *cpuc, struct perf_event *event)
>> > +{
>> > +       struct hw_perf_event *hwc = &event->hw;
>> > +       unsigned int e = hwc->config & ARCH_PERFMON_EVENTSEL_EVENT;
>> > +       struct event_constraint *c;
>> > +       struct intel_percore *pc;
>> > +       struct er_account *era;
>> > +       int i;
>> > +       int free_slot;
>> > +       int found;
>> > +
>> > +       if (!x86_pmu.percore_constraints || hwc->extra_alloc)
>> > +               return NULL;
>> > +
>> > +       for (c = x86_pmu.percore_constraints; c->cmask; c++) {
>> > +               if (e != c->code)
>> > +                       continue;
>> > +
>> > +               /*
>> > +                * Allocate resource per core.
>> > +                */
>> > +               c = NULL;
>>
>> Not sure I understand this c = NULL, given you hardcoded return NULL
>> outside of the
>> loop. I forgot to mention this earlier.
>
> Right, that is redundant.
> Remove it.
>
>>
>> > +               pc = cpuc->per_core;
>> > +               if (!pc)
>> > +                       break;
>> > +               c = &emptyconstraint;
>> > +               raw_spin_lock(&pc->lock);
>> > +               free_slot = -1;
>> > +               found = 0;
>> > +               for (i = 0; i < MAX_EXTRA_REGS; i++) {
>> > +                       era = &pc->regs[i];
>> > +                       if (era->ref > 0 && hwc->extra_reg == era->extra_reg) {
>> > +                               /* Allow sharing same config */
>> > +                               if (hwc->extra_config == era->extra_config) {
>> > +                                       era->ref++;
>> > +                                       cpuc->percore_used = 1;
>> > +                                       hwc->extra_alloc = 1;
>> > +                                       c = NULL;
>> > +                               }
>> > +                               /* else conflict */
>> > +                               found = 1;
>> > +                               break;
>> > +                       } else if (era->ref == 0 && free_slot == -1)
>> > +                               free_slot = i;
>> > +               }
>> > +               if (!found && free_slot != -1) {
>> > +                       era = &pc->regs[free_slot];
>> > +                       era->ref = 1;
>> > +                       era->extra_reg = hwc->extra_reg;
>> > +                       era->extra_config = hwc->extra_config;
>> > +                       cpuc->percore_used = 1;
>> > +                       hwc->extra_alloc = 1;
>> > +                       c = NULL;
>> > +               }
>> > +               raw_spin_unlock(&pc->lock);
>> > +               return c;
>> > +       }
>> > +
>> > +       return NULL;
>> > +}
>> > +
>> > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
>> > index 8ceb5a6..48d966a 100644
>> > --- a/include/linux/perf_event.h
>> > +++ b/include/linux/perf_event.h
>> > @@ -225,8 +225,14 @@ struct perf_event_attr {
>> >        };
>> >
>> >        __u32                   bp_type;
>> > -       __u64                   bp_addr;
>> > -       __u64                   bp_len;
>> > +       union {
>> > +               __u64           bp_addr;
>> > +               __u64           config1; /* extension of config0 */
>> > +       };
>> > +       union {
>> > +               __u64           bp_len;
>> > +               __u64           config2; /* extension of config1 */
>> > +       };
>> >  };
>> >
>> I don't see where those config0 or config1 are coming from.
>
> config0 means perf_event_attr::config.
>
yes.

> Peter suggested to extend the attr config space.
> http://marc.info/?l=linux-kernel&m=129838808907525&w=2
>
Ok, I get it, it is cascading. that's fine.