perf/x86/intel: Support branch counters logging

The branch counters logging (A.K.A LBR event logging) introduces a
per-counter indication of precise event occurrences in LBRs. It can
provide a means to attribute exposed retirement latency to combinations
of events across a block of instructions. It also provides a means of
attributing Timed LBR latencies to events.

The feature is first introduced on SRF/GRR. It is an enhancement of the
ARCH LBR. It adds new fields in the LBR_INFO MSRs to log the occurrences
of events on the GP counters. The information is displayed by the order
of counters.

The design proposed in this patch requires that the events which are
logged must be in a group with the event that has LBR. If there are
more than one LBR group, the counters logging information only from the
current group (overflowed) are stored for the perf tool, otherwise the
perf tool cannot know which and when other groups are scheduled
especially when multiplexing is triggered. The user can ensure it uses
the maximum number of counters that support LBR info (4 by now) by
making the group large enough.

The HW only logs events by the order of counters. The order may be
different from the order of enabling which the perf tool can understand.
When parsing the information of each branch entry, convert the counter
order to the enabled order, and store the enabled order in the extension
space.

Unconditionally reset LBRs for an LBR event group when it's deleted. The
logged counter information is only valid for the current LBR group. If
another LBR group is scheduled later, the information from the stale
LBRs would be otherwise wrongly interpreted.

Add a sanity check in intel_pmu_hw_config(). Disable the feature if other
counter filters (inv, cmask, edge, in_tx) are set or LBR call stack mode
is enabled. (For the LBR call stack mode, we cannot simply flush the
LBR, since it will break the call stack. Also, there is no obvious usage
with the call stack mode for now.)

Only applying the PERF_SAMPLE_BRANCH_COUNTERS doesn't require any branch
stack setup.

Expose the maximum number of supported counters and the width of the
counters into the sysfs. The perf tool can use the information to parse
the logged counters in each branch.

Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20231025201626.3000228-5-kan.liang@linux.intel.com

1 files changed, 4 insertions, 0 deletions

diff --git a/arch/x86/include/asm/perf_event.h b/arch/x86/include/asm/perf_event.h
index 2618ec7c3d1d..3736b8a46c04 100644
--- a/arch/x86/include/asm/perf_event.h
+++ b/arch/x86/include/asm/perf_event.h
@@ -31,6 +31,7 @@
 #define ARCH_PERFMON_EVENTSEL_ENABLE			(1ULL << 22)
 #define ARCH_PERFMON_EVENTSEL_INV			(1ULL << 23)
 #define ARCH_PERFMON_EVENTSEL_CMASK			0xFF000000ULL
+#define ARCH_PERFMON_EVENTSEL_BR_CNTR			(1ULL << 35)
 
 #define INTEL_FIXED_BITS_MASK				0xFULL
 #define INTEL_FIXED_BITS_STRIDE			4
@@ -223,6 +224,9 @@ union cpuid28_ecx {
 		unsigned int    lbr_timed_lbr:1;
 		/* Branch Type Field Supported */
 		unsigned int    lbr_br_type:1;
+		unsigned int	reserved:13;
+		/* Branch counters (Event Logging) Supported */
+		unsigned int	lbr_counters:4;
 	} split;
 	unsigned int            full;
 };