linux-kernel - Re: [PATCH v1 2/2] perf/x86: add cycles:pp alias for Intel Atom

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Date:	Wed, 2 Dec 2015 14:28:27 -0800
From:	Stephane Eranian <eranian@...gle.com>
To:	"Liang, Kan" <kan.liang@...el.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"acme@...hat.com" <acme@...hat.com>,
	"peterz@...radead.org" <peterz@...radead.org>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>
Subject: Re: [PATCH v1 2/2] perf/x86: add cycles:pp alias for Intel Atom

On Wed, Dec 2, 2015 at 11:37 AM, Liang, Kan <kan.liang@...el.com> wrote:
>
>
>> -----Original Message-----
>> From: Stephane Eranian [mailto:eranian@...gle.com]
>> Sent: Wednesday, December 02, 2015 1:28 PM
>> To: linux-kernel@...r.kernel.org
>> Cc: acme@...hat.com; peterz@...radead.org; mingo@...e.hu;
>> ak@...ux.intel.com; Liang, Kan
>> Subject: [PATCH v1 2/2] perf/x86: add cycles:pp alias for Intel Atom
>>
>> This patch updates the PEBS support for Intel Atom to provide an alias for
>> the cycles:pp event used by perf record/top by default nowadays.
>>
>> On Atom only INST_RETIRED:ANY supports PEBS, so we use this event
>> instead with a large cmask to count cycles.
>>
>> Signed-off-by: Stephane Eranian <eranian@...gle.com>
>> ---
>>  arch/x86/kernel/cpu/perf_event_intel.c    | 30
>> ++++++++++++++++++++++++++++++
>>  arch/x86/kernel/cpu/perf_event_intel_ds.c |  2 ++
>>  2 files changed, 32 insertions(+)
>>
>> diff --git a/arch/x86/kernel/cpu/perf_event_intel.c
>> b/arch/x86/kernel/cpu/perf_event_intel.c
>> index 61f2577..7ff1e30 100644
>> --- a/arch/x86/kernel/cpu/perf_event_intel.c
>> +++ b/arch/x86/kernel/cpu/perf_event_intel.c
>> @@ -2475,6 +2475,35 @@ static void intel_pebs_aliases_snb(struct
>> perf_event *event)
>>       }
>>  }
>>
>> +static void intel_pebs_aliases_atom(struct perf_event *event) {
>> +     if ((event->hw.config & X86_RAW_EVENT_MASK) == 0x003c) {
>> +             /*
>> +              * Use an alternative encoding for
>> CPU_CLK_UNHALTED.THREAD_P
>> +              * (0x003c) so that we can use it with PEBS.
>> +              *
>> +              * The regular CPU_CLK_UNHALTED.THREAD_P event
>> (0x003c) isn't
>> +              * PEBS capable. However we can use UOPS_RETIRED.ALL
>> +              * (0x01c2), which is a PEBS capable event, to get the same
>
> The comment isn't consistent with the code.
>
>> +              * count.
>> +              *
>> +              * INST_RETIRED.ANY counts the number of cycles that
>> retires
>> +              * CNTMASK instructions. By setting CNTMASK to a value
>> (16)
>> +              * larger than the maximum number of instructions that
>> can be
>> +              * retired per cycle (4) and then inverting the condition, we
>> +              * count all cycles that retire 16 or less instructions, which
>> +              * is every cycle.
>> +              *
>> +              * Thereby we gain a PEBS capable cycle counter.
>> +              */
>> +             u64 alt_config =
>> X86_CONFIG(.event=0xc0, .umask=0x00, .inv=1,
>> +.cmask=16);
>> +
>> +             alt_config |= (event->hw.config &
>> ~X86_RAW_EVENT_MASK);
>> +             event->hw.config = alt_config;
>> +     }
>> +}
>> +
>> +
>>  static unsigned long intel_pmu_free_running_flags(struct perf_event
>> *event)  {
>>       unsigned long flags = x86_pmu.free_running_flags; @@ -3332,6
>> +3361,7 @@ __init int intel_pmu_init(void)
>>
>>               x86_pmu.event_constraints =
>> intel_gen_event_constraints;
>>               x86_pmu.pebs_constraints =
>> intel_atom_pebs_event_constraints;
>> +             x86_pmu.pebs_aliases = intel_pebs_aliases_atom;
>
> intel_pebs_aliases_atom looks the same as intel_pebs_aliases_core2.
> Why not reuse the existing intel_pebs_aliases_core2?
>
Sure, will do this in V2.
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