Re: [PATCH 4/9] perf/x86/intel: Support hardware TopDown metrics

["Liang, Kan" <kan.liang@linux.intel.com>]

On 5/29/2019 12:58 PM, Peter Zijlstra wrote:
> On Wed, May 29, 2019 at 10:42:10AM -0400, Liang, Kan wrote:
>> On 5/29/2019 3:54 AM, Peter Zijlstra wrote:
> 
>>> cd09c0c40a97 ("perf events: Enable raw event support for Intel unhalted_reference_cycles event")
>>>
>>> We used the fake event=0x00, umask=0x03 for CPU_CLK_UNHALTED.REF_TSC,
>>> because that was not available as a generic event, *until now* it seems.
>>> I see ICL actually has it as a generic event, which means we need to fix
>>> up the constraint mask for that differently.
>>>
>>
>> There is no change for REF_TSC on ICL.
> 
> Well, if I look at the SDM for May'19 (latest afaict), Volume 3, Chapter
> 19.3 'Performance Monitoring Events for Future Intel (C) Core(tm)
> Processors' the table lists:
> 
>   Event Num.	Umask Value	Event Mask Mnemonic
> 
>   00H		03H		CPU_CLK_UNHALTED.REF_TSC
> 
> as a generic event, without constraints, unlike any of the preceding
> uarchs, where that event was not available except through FIXED2.
> 
> That is most certainly a change.

I checked with our internal team. They confirmed that there is no change 
for REF_TSC on ICL.
They will fix the comment in the next SDM update.
Thanks for bringing this up.

> 
>>> But note that for all previous uarchs this event did not in fact exist.
>>>
>>> It appears the TOPDOWN.SLOTS thing, which is available in in FIXED3 is
>>> event=0x00, umask=0x04, is indeed a generic event too.
>>
>> The SLOTS do have a generic event, TOPDOWN.SLOTS_P, event=0xA4, umask=0x1.
>>
>> I think we need a fix as below for ICL, so the SLOT event can be extended to
>> generic event.
>> -	FIXED_EVENT_CONSTRAINT(0x0400, 3),	/* SLOTS */
>> +	FIXED_EVENT_CONSTRAINT(0x01a4, 3),	/* TOPDOWN.SLOTS */
> 
> Then WTH is that 00H, 04H event listed in the table? Note the distinct
> lack of 'Fixed Counter' or any other contraints in the 'Comments'
> column.
>

TOPDOWN.SLOTS(0x0400) is only available on FIXED3. It's not a generic 
event. The equivalent event for GP counters is TOPDOWN.SLOTS_P (0x01a4).
But it's not architectural event.
So I think the best way is to force TOPDOWN.SLOTS(0x0400) only in 
FIXED3. The patch as below will do so.


 From 22e3ed25340e4f46685a059cf2184747a3e02a47 Mon Sep 17 00:00:00 2001
From: Kan Liang <kan.liang@linux.intel.com>
Date: Tue, 4 Jun 2019 10:36:08 -0700
Subject: [PATCH] perf/x86/intel: Set correct mask for TOPDOWN.SLOTS

TOPDOWN.SLOTS(0x0400) is not a generic event. It is only available on
fixed counter3.

Don't extend its mask to generic counters.

Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
---
  arch/x86/events/intel/core.c      | 6 ++++--
  arch/x86/include/asm/perf_event.h | 5 +++++
  2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index 4377bf6a6f82..f30d02830921 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -5066,12 +5066,14 @@ __init int intel_pmu_init(void)

  	if (x86_pmu.event_constraints) {
  		/*
-		 * event on fixed counter2 (REF_CYCLES) only works on this
+		 * event on fixed counter2 (REF_CYCLES) and
+		 * fixed counter3 (TOPDOWN.SLOTS) only work on this
  		 * counter, so do not extend mask to generic counters
  		 */
  		for_each_event_constraint(c, x86_pmu.event_constraints) {
  			if (c->cmask == FIXED_EVENT_FLAGS
-			    && c->idxmsk64 != INTEL_PMC_MSK_FIXED_REF_CYCLES) {
+			    && c->idxmsk64 != INTEL_PMC_MSK_FIXED_REF_CYCLES
+			    && c->idxmsk64 != INTEL_PMC_MSK_FIXED_SLOTS) {
  				c->idxmsk64 |= (1ULL << x86_pmu.num_counters) - 1;
  			}
  			c->idxmsk64 &=
diff --git a/arch/x86/include/asm/perf_event.h 
b/arch/x86/include/asm/perf_event.h
index 1392d5e6e8d6..457d35a75ad3 100644
--- a/arch/x86/include/asm/perf_event.h
+++ b/arch/x86/include/asm/perf_event.h
@@ -167,6 +167,11 @@ struct x86_pmu_capability {
  #define INTEL_PMC_IDX_FIXED_REF_CYCLES	(INTEL_PMC_IDX_FIXED + 2)
  #define INTEL_PMC_MSK_FIXED_REF_CYCLES	(1ULL << 
INTEL_PMC_IDX_FIXED_REF_CYCLES)

+/* TOPDOWN.SLOTS: */
+#define MSR_ARCH_PERFMON_FIXED_CTR3	0x30c
+#define INTEL_PMC_IDX_FIXED_SLOTS	(INTEL_PMC_IDX_FIXED + 3)
+#define INTEL_PMC_MSK_FIXED_SLOTS	(1ULL << INTEL_PMC_IDX_FIXED_SLOTS)
+
  /*
   * We model BTS tracing as another fixed-mode PMC.
   *
-- 
2.14.5

Thanks,
Kan