linux-kernel - [PATCH] perf/x86/intel/ds: fix precise store latency handling

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Message-Id: <20220818054613.1548130-1-eranian@google.com>
Date:   Wed, 17 Aug 2022 22:46:13 -0700
From:   Stephane Eranian <eranian@...gle.com>
To:     linux-kernel@...r.kernel.org
Cc:     peterz@...radead.org, kan.liang@...el.com, ak@...ux.intel.com,
        acme@...hat.com, namhyung@...nel.org, irogers@...gle.com
Subject: [PATCH] perf/x86/intel/ds: fix precise store latency handling

With the existing code in store_latency_data(), the memory operation (mem_op)
returned to the user is always OP_LOAD where in fact, it should be OP_STORE.
This comes from the fact that the function is simply grabbing the information
from a data source map which covers only load accesses. Intel 12th gen CPU
offers precise store sampling that captures both the data source and latency.
Therefore it can use the data source mapping table but must override the
memory operation to reflect stores instead of loads.

Fixes: 61b985e3e775 ("perf/x86/intel: Add perf core PMU support for Sapphire Rapids")

Signed-off-by: Stephane Eranian <eranian@...gle.com>
---
 arch/x86/events/intel/ds.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c
index ba60427caa6d..189fc6e9ea65 100644
--- a/arch/x86/events/intel/ds.c
+++ b/arch/x86/events/intel/ds.c
@@ -291,6 +291,7 @@ static u64 load_latency_data(struct perf_event *event, u64 status)
 static u64 store_latency_data(struct perf_event *event, u64 status)
 {
 	union intel_x86_pebs_dse dse;
+	union perf_mem_data_src src;
 	u64 val;
 
 	dse.val = status;
@@ -304,7 +305,14 @@ static u64 store_latency_data(struct perf_event *event, u64 status)
 
 	val |= P(BLK, NA);
 
-	return val;
+	/*
+	 * the pebs_data_source table is only for loads
+	 * so override the mem_op to say STORE instead
+	 */
+	src.val = val;
+	src.mem_op = P(OP,STORE);
+
+	return src.val;
 }
 
 struct pebs_record_core {
-- 
2.37.1.595.g718a3a8f04-goog