linux-kernel - Re: [PATCH RESEND V5 1/6] perf, amd: Rework northbridge event constraints handler

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Date:	Fri, 25 Jan 2013 11:52:59 +0100
From:	Stephane Eranian <eranian@...gle.com>
To:	Jacob Shin <jacob.shin@....com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86 <x86@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	LKML <linux-kernel@...r.kernel.org>,
	Robert Richter <rric@...nel.org>
Subject: Re: [PATCH RESEND V5 1/6] perf, amd: Rework northbridge event
 constraints handler

On Thu, Jan 10, 2013 at 8:50 PM, Jacob Shin <jacob.shin@....com> wrote:
> From: Robert Richter <rric@...nel.org>
>
> Code simplification. No functional changes.
>
> Signed-off-by: Robert Richter <rric@...nel.org>
> Signed-off-by: Jacob Shin <jacob.shin@....com>

Acked-by: Stephane Eranian <eranian@...gle.com>

> ---
>  arch/x86/kernel/cpu/perf_event_amd.c |   68 +++++++++++++---------------------
>  1 file changed, 26 insertions(+), 42 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/perf_event_amd.c b/arch/x86/kernel/cpu/perf_event_amd.c
> index c93bc4e..e7963c7 100644
> --- a/arch/x86/kernel/cpu/perf_event_amd.c
> +++ b/arch/x86/kernel/cpu/perf_event_amd.c
> @@ -256,9 +256,8 @@ amd_get_event_constraints(struct cpu_hw_events *cpuc, struct perf_event *event)
>  {
>         struct hw_perf_event *hwc = &event->hw;
>         struct amd_nb *nb = cpuc->amd_nb;
> -       struct perf_event *old = NULL;
> -       int max = x86_pmu.num_counters;
> -       int i, j, k = -1;
> +       struct perf_event *old;
> +       int idx, new = -1;
>
>         /*
>          * if not NB event or no NB, then no constraints
> @@ -276,48 +275,33 @@ amd_get_event_constraints(struct cpu_hw_events *cpuc, struct perf_event *event)
>          * because of successive calls to x86_schedule_events() from
>          * hw_perf_group_sched_in() without hw_perf_enable()
>          */
> -       for (i = 0; i < max; i++) {
> -               /*
> -                * keep track of first free slot
> -                */
> -               if (k == -1 && !nb->owners[i])
> -                       k = i;
> +       for (idx = 0; idx < x86_pmu.num_counters; idx++) {
> +               if (new == -1 || hwc->idx == idx)
> +                       /* assign free slot, prefer hwc->idx */
> +                       old = cmpxchg(nb->owners + idx, NULL, event);
> +               else if (nb->owners[idx] == event)
> +                       /* event already present */
> +                       old = event;
> +               else
> +                       continue;
> +
> +               if (old && old != event)
> +                       continue;
> +
> +               /* reassign to this slot */
> +               if (new != -1)
> +                       cmpxchg(nb->owners + new, event, NULL);
> +               new = idx;
>
>                 /* already present, reuse */
> -               if (nb->owners[i] == event)
> -                       goto done;
> -       }
> -       /*
> -        * not present, so grab a new slot
> -        * starting either at:
> -        */
> -       if (hwc->idx != -1) {
> -               /* previous assignment */
> -               i = hwc->idx;
> -       } else if (k != -1) {
> -               /* start from free slot found */
> -               i = k;
> -       } else {
> -               /*
> -                * event not found, no slot found in
> -                * first pass, try again from the
> -                * beginning
> -                */
> -               i = 0;
> -       }
> -       j = i;
> -       do {
> -               old = cmpxchg(nb->owners+i, NULL, event);
> -               if (!old)
> +               if (old == event)
>                         break;
> -               if (++i == max)
> -                       i = 0;
> -       } while (i != j);
> -done:
> -       if (!old)
> -               return &nb->event_constraints[i];
> -
> -       return &emptyconstraint;
> +       }
> +
> +       if (new == -1)
> +               return &emptyconstraint;
> +
> +       return &nb->event_constraints[new];
>  }
>
>  static struct amd_nb *amd_alloc_nb(int cpu)
> --
> 1.7.9.5
>
>
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