Re: [PATCH] perf_events: fix bug in hw_perf_enable()

[Stephane Eranian <eranian@google.com>]

On Mon, Feb 1, 2010 at 4:35 PM, Peter Zijlstra <peterz@infradead.org> wrote:
> On Mon, 2010-02-01 at 14:50 +0200, Stephane Eranian wrote:
>>       We cannot assume that because hwc->idx == assign[i], we
>>       can avoid reprogramming the counter in hw_perf_enable().
>>
>>       The event may have been scheduled out and another event
>>       may have been programmed into this counter. Thus, we need
>>       a more robust way of verifying if the counter still
>>       contains config/data related to an event.
>>
>>       This patch adds a generation number to each counter on each
>>       cpu. Using this mechanism we can verify reliabilty whether the
>>       content of a counter corresponds to an event.
>>
>>       Signed-off-by: Stephane Eranian <eranian@google.com>
>
> Thanks, got it.
>
> btw, I've also added the below, from what I can make from the docs fixed
> counter 2 is identical to arch perf event 0x013c, as per table A-1 and
> A-7. Both are called CPU_CLK_UNHALTED.REF, except for Core2, where
> 0x013c is called CPU_CLK_UNHALTED.BUS.
>

If you measure 0x013c in a generic counter or in fixed counter 2
it will count the same thing but not at the same rate.
This is true on Core2, Atom, Nehalem, Westmere. The ratio is the
clock/bus ratio.

This goes back to an earlier discussion where I was asking about
the meaning of the generic PMU events and in particular
PERF_COUNT_HW_CPU_CYCLES. Which of the 3 distinct cycle
events (unhalted_core_cycles, unhalted_reference_cycles, bus_cycles)
does not correspond to?



> ---
> Subject: perf_events, x86: Fixup fixed counter constraints
> From: Peter Zijlstra <a.p.zijlstra@chello.nl>
> Date: Mon Feb 01 15:36:30 CET 2010
>
> Patch 1da53e0230 ("perf_events, x86: Improve x86 event scheduling")
> lost us one of the fixed purpose counters and then ed8777fc13
> ("perf_events, x86: Fix event constraint masks") broke it even
> further.
>
> Widen the fixed event mask to event+umask and specify the full config
> for each of the 3 fixed purpose counters. Then let the init code fill
> out the placement for the GP regs based on the cpuid info.
>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
> LKML-Reference: <new-submission>
> ---
>  arch/x86/include/asm/perf_event.h |    2 +-
>  arch/x86/kernel/cpu/perf_event.c  |   38 ++++++++++++++++++++++++++++++--------
>  2 files changed, 31 insertions(+), 9 deletions(-)
>
> Index: linux-2.6/arch/x86/include/asm/perf_event.h
> ===================================================================
> --- linux-2.6.orig/arch/x86/include/asm/perf_event.h
> +++ linux-2.6/arch/x86/include/asm/perf_event.h
> @@ -50,7 +50,7 @@
>         INTEL_ARCH_INV_MASK| \
>         INTEL_ARCH_EDGE_MASK|\
>         INTEL_ARCH_UNIT_MASK|\
> -        INTEL_ARCH_EVTSEL_MASK)
> +        INTEL_ARCH_EVENT_MASK)
>
>  #define ARCH_PERFMON_UNHALTED_CORE_CYCLES_SEL                0x3c
>  #define ARCH_PERFMON_UNHALTED_CORE_CYCLES_UMASK                (0x00 << 8)
> Index: linux-2.6/arch/x86/kernel/cpu/perf_event.c
> ===================================================================
> --- linux-2.6.orig/arch/x86/kernel/cpu/perf_event.c
> +++ linux-2.6/arch/x86/kernel/cpu/perf_event.c
> @@ -243,8 +243,18 @@ static struct event_constraint intel_cor
>
>  static struct event_constraint intel_core2_event_constraints[] =
>  {
> -       FIXED_EVENT_CONSTRAINT(0xc0, (0x3|(1ULL<<32))), /* INSTRUCTIONS_RETIRED */
> -       FIXED_EVENT_CONSTRAINT(0x3c, (0x3|(1ULL<<33))), /* UNHALTED_CORE_CYCLES */
> +       FIXED_EVENT_CONSTRAINT(0x00c0, 1ULL << 32), /* INST_RETIRED.ANY */
> +       FIXED_EVENT_CONSTRAINT(0x003c, 1ULL << 33), /* CPU_CLK_UNHALTED.CORE */
> +       /*
> +        * FIXED_EVENT_CONSTRAINT(0x013c, 1ULL << 34),  CPU_CLK_UNHALTED.REF
> +        *
> +        * Core2 has Fixed Counter 2 listed as CPU_CLK_UNHALTED.REF and event
> +        * 0x013c as CPU_CLK_UNHALTED.BUS and specifies there is a fixed
> +        * ratio between these counters.
> +        *
> +        * TODO: find/measure the fixed ratio and apply it so that we can
> +        * enable this fixed purpose counter in a transparent way.
> +        */
>        INTEL_EVENT_CONSTRAINT(0x10, 0x1), /* FP_COMP_OPS_EXE */
>        INTEL_EVENT_CONSTRAINT(0x11, 0x2), /* FP_ASSIST */
>        INTEL_EVENT_CONSTRAINT(0x12, 0x2), /* MUL */
> @@ -259,8 +269,9 @@ static struct event_constraint intel_cor
>
>  static struct event_constraint intel_nehalem_event_constraints[] =
>  {
> -       FIXED_EVENT_CONSTRAINT(0xc0, (0xf|(1ULL<<32))), /* INSTRUCTIONS_RETIRED */
> -       FIXED_EVENT_CONSTRAINT(0x3c, (0xf|(1ULL<<33))), /* UNHALTED_CORE_CYCLES */
> +       FIXED_EVENT_CONSTRAINT(0x00c0, 1ULL << 32), /* INST_RETIRED.ANY */
> +       FIXED_EVENT_CONSTRAINT(0x003c, 1ULL << 33), /* CPU_CLK_UNHALTED.CORE */
> +       FIXED_EVENT_CONSTRAINT(0x013c, 1ULL << 34), /* CPU_CLK_UNHALTED.REF */
>        INTEL_EVENT_CONSTRAINT(0x40, 0x3), /* L1D_CACHE_LD */
>        INTEL_EVENT_CONSTRAINT(0x41, 0x3), /* L1D_CACHE_ST */
>        INTEL_EVENT_CONSTRAINT(0x42, 0x3), /* L1D_CACHE_LOCK */
> @@ -274,8 +285,9 @@ static struct event_constraint intel_neh
>
>  static struct event_constraint intel_westmere_event_constraints[] =
>  {
> -       FIXED_EVENT_CONSTRAINT(0xc0, (0xf|(1ULL<<32))), /* INSTRUCTIONS_RETIRED */
> -       FIXED_EVENT_CONSTRAINT(0x3c, (0xf|(1ULL<<33))), /* UNHALTED_CORE_CYCLES */
> +       FIXED_EVENT_CONSTRAINT(0x00c0, 1ULL << 32), /* INST_RETIRED.ANY */
> +       FIXED_EVENT_CONSTRAINT(0x003c, 1ULL << 33), /* CPU_CLK_UNHALTED.CORE */
> +       FIXED_EVENT_CONSTRAINT(0x013c, 1ULL << 34), /* CPU_CLK_UNHALTED.REF */
>        INTEL_EVENT_CONSTRAINT(0x51, 0x3), /* L1D */
>        INTEL_EVENT_CONSTRAINT(0x60, 0x1), /* OFFCORE_REQUESTS_OUTSTANDING */
>        INTEL_EVENT_CONSTRAINT(0x63, 0x3), /* CACHE_LOCK_CYCLES */
> @@ -284,8 +296,9 @@ static struct event_constraint intel_wes
>
>  static struct event_constraint intel_gen_event_constraints[] =
>  {
> -       FIXED_EVENT_CONSTRAINT(0xc0, (0x3|(1ULL<<32))), /* INSTRUCTIONS_RETIRED */
> -       FIXED_EVENT_CONSTRAINT(0x3c, (0x3|(1ULL<<33))), /* UNHALTED_CORE_CYCLES */
> +       FIXED_EVENT_CONSTRAINT(0x00c0, 1ULL << 32), /* INST_RETIRED.ANY */
> +       FIXED_EVENT_CONSTRAINT(0x003c, 1ULL << 33), /* CPU_CLK_UNHALTED.CORE */
> +       FIXED_EVENT_CONSTRAINT(0x013c, 1ULL << 34), /* CPU_CLK_UNHALTED.REF */
>        EVENT_CONSTRAINT_END
>  };
>
> @@ -2602,6 +2615,7 @@ static void __init pmu_check_apic(void)
>
>  void __init init_hw_perf_events(void)
>  {
> +       struct event_constraint *c;
>        int err;
>
>        pr_info("Performance Events: ");
> @@ -2650,6 +2664,14 @@ void __init init_hw_perf_events(void)
>                __EVENT_CONSTRAINT(0, (1ULL << x86_pmu.num_events) - 1,
>                                   0, x86_pmu.num_events);
>
> +       for_each_event_constraint(c, x86_pmu.event_constraints) {
> +               if (c->cmask != INTEL_ARCH_FIXED_MASK)
> +                       continue;
> +
> +               c->idxmsk64[0] |= (1ULL << x86_pmu.num_events) - 1;
> +               c->weight += x86_pmu.num_events;
> +       }
> +
>        pr_info("... version:                %d\n",     x86_pmu.version);
>        pr_info("... bit width:              %d\n",     x86_pmu.event_bits);
>        pr_info("... generic registers:      %d\n",     x86_pmu.num_events);
>
>
>



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Stephane Eranian  | EMEA Software Engineering
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