Re: [PATCH 1/2] perf-events: Add support for supplementary event registers v2

[Peter Zijlstra <a.p.zijlstra@chello.nl>]

On Fri, 2010-11-12 at 17:55 +0100, Andi Kleen wrote:
>  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;
> +
> +       if (!x86_pmu.percore_constraints)
> +               return NULL;
> +
> +       for (c = x86_pmu.percore_constraints; c->cmask; c++) { 
> +               if (e != c->code)
> +                       continue;
> +
> +               c = NULL;
> +
> +               /*
> +                * Allocate resource per core.
> +                * Currently only one such per core resource can be allocated.
> +                */
> +               pc = cpuc->per_core;
> +               if (!pc)
> +                       break;
> +               raw_spin_lock(&pc->lock);
> +               if (pc->ref > 0) {
> +                       /* Allow identical settings */
> +                       if (hwc->config == pc->config &&
> +                           hwc->extra_reg == pc->extra_reg &&
> +                           hwc->extra_config == pc->extra_config) {

Hrmm,. this doesn't really scale right wrt multiple extra_regs.

You made the extra_regs thing fairly extensible, but the above doesn't
really work well if there's multiple extra regs (say OFFCORE and
LBR_CONFIG -- possibly even the two OFFCORE regs present on westmere).

It basically needs a per-core state for each extra_reg possible.

> +                               pc->ref++;
> +                               cpuc->percore_used = 1;
> +                       } else {
> +                               /* Deny due to conflict */
> +                               c = &emptyconstraint;
> +                       }
> +               } else {
> +                       pc->config = hwc->config;
> +                       pc->extra_reg = hwc->extra_reg;
> +                       pc->extra_config = hwc->extra_config;
> +                       pc->ref = 1;
> +                       cpuc->percore_used = 1;
> +               }
> +               raw_spin_unlock(&pc->lock);
> +               return c;
> +       }
> +
> +       return NULL;
> +}