[kvm-unit-tests patch v6 15/18] x86: pmu: Adjust lower boundary of llc-misses event to 0 for legacy CPUs

Dapeng Mi
2024-09-14T07:01:52Z

For these legacy Intel CPUs without clflush/clflushopt support, there is
on way to force to trigger a LLC miss and the measured llc misses is
possible to be 0. Thus adjust the lower boundary of llc-misses event to
0 to avoid possible false positive.

Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
---
x86/pmu.c | 10 ++++++++++
1 file changed, 10 insertions(+)

diff --git a/x86/pmu.c b/x86/pmu.c
index c9160423..47b6305d 100644
--- a/x86/pmu.c
+++ b/x86/pmu.c
@@ -82,6 +82,7 @@ struct pmu_event {
enum {
INTEL_INSTRUCTIONS_IDX = 1,
INTEL_REF_CYCLES_IDX = 2,
+ INTEL_LLC_MISSES_IDX = 4,
INTEL_BRANCHES_IDX = 5,
};

@@ -892,6 +893,15 @@ int main(int ac, char **av)
gp_events_size = sizeof(intel_gp_events)/sizeof(intel_gp_events[0]);
instruction_idx = INTEL_INSTRUCTIONS_IDX;
branch_idx = INTEL_BRANCHES_IDX;
+
+ /*
+ * For legacy Intel CPUS without clflush/clflushopt support,
+ * there is no way to force to trigger a LLC miss, thus set
+ * the minimum value to 0 to avoid false positives.
+ */
+ if (!this_cpu_has(X86_FEATURE_CLFLUSH))
+ gp_events[INTEL_LLC_MISSES_IDX].min = 0;
+
report_prefix_push("Intel");
set_ref_cycle_expectations();
} else {
--
2.40.1