linux-kernel - [RFC] perf/x86/intel/uncore: pmu->type->single

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Message-ID: <20161130105105.GA25720@krava>
Date:   Wed, 30 Nov 2016 11:51:05 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     "Liang, Kan" <kan.liang@...el.com>
Cc:     Andi Kleen <andi@...stfloor.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Jiri Olsa <jolsa@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Michael Petlan <mpetlan@...hat.com>
Subject: [RFC] perf/x86/intel/uncore: pmu->type->single_fixed question

hi,
I'm trying to find out some documentation background for this part of uncore code:

---
static int uncore_pmu_event_init(struct perf_event *event)
{
        ...
        if (event->attr.config == UNCORE_FIXED_EVENT) {
                /* no fixed counter */
                if (!pmu->type->fixed_ctl)
                        return -EINVAL;
                /*
                 * if there is only one fixed counter, only the first pmu
                 * can access the fixed counter
                 */
                if (pmu->type->single_fixed && pmu->pmu_idx > 0)
                        return -EINVAL;
        ...
---

that for some uncore types (those with pmu->type->single_fixed) only
the first pmu (code_id == 0) will allow to touch the clocktick event

other cores boxes will not allow to open clocktick event, eventhough
it's announced via /sys/../events/.. 

I'm probably missing some HW logic of specific boxes that would explain
that, but I can't find it.

thanks for info,
jirka