[PATCH] x86/pmu: Disable inlining of measure()

Bill Wendling
2022-06-01T16:30:22Z

From: Bill Wendling <isanbard@gmail.com>

Clang can be more aggressive at inlining than GCC and will fully inline
calls to measure(). This can mess with the counter overflow check. To
set up the PMC overflow, check_counter_overflow() first records the
number of instructions retired in an invocation of measure() and checks
to see that subsequent calls to measure() retire the same number of
instructions. If inlining occurs, those numbers can be different and the
overflow test fails.

FAIL: overflow: cntr-0
PASS: overflow: status-0
PASS: overflow: status clear-0
PASS: overflow: irq-0
FAIL: overflow: cntr-1
PASS: overflow: status-1
PASS: overflow: status clear-1
PASS: overflow: irq-1
FAIL: overflow: cntr-2
PASS: overflow: status-2
PASS: overflow: status clear-2
PASS: overflow: irq-2
FAIL: overflow: cntr-3
PASS: overflow: status-3
PASS: overflow: status clear-3
PASS: overflow: irq-3

Disabling inlining of measure() keeps the assumption that all calls to
measure() retire the same number of instructions.

Cc: Jim Mattson <jmattson@google.com>
Signed-off-by: Bill Wendling <morbo@google.com>
---
x86/pmu.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/x86/pmu.c b/x86/pmu.c
index a46bdbf4788c..bbfd268aafa4 100644
--- a/x86/pmu.c
+++ b/x86/pmu.c
@@ -211,7 +211,7 @@ static void stop_event(pmu_counter_t *evt)
evt->count = rdmsr(evt->ctr);
}

-static void measure(pmu_counter_t *evt, int count)
+static noinline void measure(pmu_counter_t *evt, int count)
{
int i;
for (i = 0; i < count; i++)
--
2.36.1.255.ge46751e96f-goog