Re: [Qemu-devel] [PATCH v8 13/13] target/arm: Send interrupts on PMU counter overflow

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

On 11/20/18 1:26 PM, Aaron Lindsay wrote:
> Setup a QEMUTimer to get a callback when we expect counters to next
> overflow and trigger an interrupt at that time.
> 
> Signed-off-by: Aaron Lindsay <alindsay@codeaurora.org>
> Signed-off-by: Aaron Lindsay <alindsay@os.amperecomputing.com>
> ---
>  target/arm/cpu.c    |  12 +++++
>  target/arm/cpu.h    |   7 +++
>  target/arm/helper.c | 126 +++++++++++++++++++++++++++++++++++++++++---
>  3 files changed, 139 insertions(+), 6 deletions(-)
> 
> diff --git a/target/arm/cpu.c b/target/arm/cpu.c
> index 208a08e867..7311a48e3c 100644
> --- a/target/arm/cpu.c
> +++ b/target/arm/cpu.c
> @@ -827,6 +827,13 @@ static void arm_cpu_finalizefn(Object *obj)
>          QLIST_REMOVE(hook, node);
>          g_free(hook);
>      }
> +#ifndef CONFIG_USER_ONLY
> +    if (arm_feature(&cpu->env, ARM_FEATURE_PMU) && cpu->pmu_timer) {

No need for two tests here.  Just check cpu->pmu_timer.
(If it's set for any reason it should be freed, surely.)

> @@ -1305,7 +1338,18 @@ void pmccntr_op_start(CPUARMState *env)
>              eff_cycles /= 64;
>          }
>  
> -        env->cp15.c15_ccnt = eff_cycles - env->cp15.c15_ccnt_delta;
> +        uint64_t new_pmccntr = eff_cycles - env->cp15.c15_ccnt_delta;
> +
> +        unsigned int overflow_bit = (env->cp15.c9_pmcr & PMCRLC) ? 63 : 31;
> +        uint64_t overflow_mask = (uint64_t)1 << overflow_bit;
> +        if (!(new_pmccntr & overflow_mask) &&
> +                (env->cp15.c15_ccnt & overflow_mask)) {

Fyi, this expression is

    env->cp15.c15_ccnt & ~new_pmccntr & overflow_mask

> +            env->cp15.c9_pmovsr |= (1 << 31);
> +            new_pmccntr &= ~overflow_mask;

Why this line?  You just checked that overflow_mask was unset in new_pmccntr above.

> @@ -1318,13 +1362,28 @@ void pmccntr_op_start(CPUARMState *env)
>  void pmccntr_op_finish(CPUARMState *env)
>  {
>      if (pmu_counter_enabled(env, 31)) {
> -        uint64_t prev_cycles = env->cp15.c15_ccnt_delta;
> +#ifndef CONFIG_USER_ONLY
> +        uint64_t delta;
> +        if (env->cp15.c9_pmcr & PMCRLC) {
> +            delta = UINT64_MAX - env->cp15.c15_ccnt + 1;
> +        } else {
> +            delta = UINT32_MAX - (uint32_t)env->cp15.c15_ccnt + 1;
> +        }

FWIW, this is the same as

    delta = -env->cp15.c15_ccnt;
    if (!(env->cp15.c9_pmcr & PMCRLC)) {
        delta = (uint32_t)delta;
    }


r~