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

Jim Mattson
2022-06-01T17:22:36Z

On Wed, Jun 1, 2022 at 9:30 AM Bill Wendling <morbo@google.com> wrote:
>
> 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>
Reviewed-by: Jim Mattson <jmattson@google.com>