Re: [PATCH v2 4/5] target/ppc: keep ins_cnt/cyc_cnt cleared if MMCR0_FC is set

[Richard Henderson <richard.henderson@linaro.org>]

On 1/3/22 10:53 AM, Daniel Henrique Barboza wrote:
> pmu_update_summaries() is not considering the case where the PMU can be
> turned off (i.e. stop counting all events) if MMCR0_FC is set,
> regardless of the other frozen counter bits state. This use case was
> covered in the late pmc_get_event(), via the also gone pmc_is_inactive(),
> that would return an invalid event if MMCR0_FC was set.
> 
> This use case is exercised by the back_to_back_ebbs_test Linux kernel
> selftests [1]. As it is today, after enabling EBB exceptions, the test
> will report an additional event-based branch being taken and will fail.
> Other tests, such as cycles_test.c, will report additional cycles being
> calculated in the counters because we're not freezing the PMU quick
> enough.
> 
> Fix pmu_update_summaries() by keeping env->ins_cnt and env->cyc_cnt
> cleared when MMCR0_FC is set.
> 
> [1] tools/testing/selftests/powerpc/pmu/ebb/back_to_back_ebbs_test.c
> 
> Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
> ---
>   target/ppc/power8-pmu.c | 5 +++++
>   1 file changed, 5 insertions(+)
> 
> diff --git a/target/ppc/power8-pmu.c b/target/ppc/power8-pmu.c
> index 7fc7d91109..73713ca2a3 100644
> --- a/target/ppc/power8-pmu.c
> +++ b/target/ppc/power8-pmu.c
> @@ -40,6 +40,10 @@ void pmu_update_summaries(CPUPPCState *env)
>       int ins_cnt = 0;
>       int cyc_cnt = 0;
>   
> +    if (mmcr0 & MMCR0_FC) {
> +        goto hflags_calc;
> +    }
> +
>       if (!(mmcr0 & MMCR0_FC14) && mmcr1 != 0) {
>           target_ulong sel;
>   
> @@ -71,6 +75,7 @@ void pmu_update_summaries(CPUPPCState *env)
>       ins_cnt |= !(mmcr0 & MMCR0_FC56) << 5;
>       cyc_cnt |= !(mmcr0 & MMCR0_FC56) << 6;
>   
> + hflags_calc:

Good catch, but should be folded into patch 1 to avoid bisection breakage.


r~