linux-kernel - Re: [RFC][PATCH 3/8] perf/x86: Simplify x86_pmu.get

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Date:   Tue, 19 Mar 2019 14:21:27 -0700
From:   Stephane Eranian <eranian@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...nel.org>, Jiri Olsa <jolsa@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>, tonyj@...e.com,
        nelson.dsouza@...el.com
Subject: Re: [RFC][PATCH 3/8] perf/x86: Simplify x86_pmu.get_constraints() interface

On Thu, Mar 14, 2019 at 6:11 AM Peter Zijlstra <peterz@...radead.org> wrote:
>
> There is a special case for validate_events() where we'll call
> x86_pmu.get_constraints(.idx=-1). It's purpose, up until recent, seems
> to be to avoid taking a previous constraint from
> cpuc->event_constraint[] in intel_get_event_constraints().
>
> (I could not find any other get_event_constraints() implementation
> using @idx)
>
> However, since that cpuc is freshly allocated, that array will in fact
> be initialized with NULL pointers, achieving the very same effect.
>
> Therefore remove this exception.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

Looks good to me.
Reviewed-by: Stephane Eranian <eranian@...gle.com>

> ---
>  arch/x86/events/core.c       |    2 +-
>  arch/x86/events/intel/core.c |    8 +++-----
>  2 files changed, 4 insertions(+), 6 deletions(-)
>
> --- a/arch/x86/events/core.c
> +++ b/arch/x86/events/core.c
> @@ -2031,7 +2031,7 @@ static int validate_event(struct perf_ev
>         if (IS_ERR(fake_cpuc))
>                 return PTR_ERR(fake_cpuc);
>
> -       c = x86_pmu.get_event_constraints(fake_cpuc, -1, event);
> +       c = x86_pmu.get_event_constraints(fake_cpuc, 0, event);
>
>         if (!c || !c->weight)
>                 ret = -EINVAL;
> --- a/arch/x86/events/intel/core.c
> +++ b/arch/x86/events/intel/core.c
> @@ -2931,11 +2931,9 @@ static struct event_constraint *
>  intel_get_event_constraints(struct cpu_hw_events *cpuc, int idx,
>                             struct perf_event *event)
>  {
> -       struct event_constraint *c1 = NULL;
> -       struct event_constraint *c2;
> +       struct event_constraint *c1, *c2;
>
> -       if (idx >= 0) /* fake does < 0 */
> -               c1 = cpuc->event_constraint[idx];
> +       c1 = cpuc->event_constraint[idx];
>
>         /*
>          * first time only
> @@ -3410,7 +3408,7 @@ tfa_get_event_constraints(struct cpu_hw_
>         /*
>          * Without TFA we must not use PMC3.
>          */
> -       if (!allow_tsx_force_abort && test_bit(3, c->idxmsk) && idx >= 0) {
> +       if (!allow_tsx_force_abort && test_bit(3, c->idxmsk)) {
>                 c = dyn_constraint(cpuc, c, idx);
>                 c->idxmsk64 &= ~(1ULL << 3);
>                 c->weight--;
>
>