Re: [PATCH] target/riscv: fix instructions count handling in icount mode

[Alistair Francis]

On Thu, Apr 11, 2024 at 9:34 PM Clément Léger <cleger@rivosinc.com> wrote:
>
> When icount is enabled, rather than returning the virtual CPU time, we
> should return the instruction count itself. Add an instructions bool
> parameter to get_ticks() to correctly return icount_get_raw() when
> icount_enabled() == 1 and instruction count is queried. This will modify
> the existing behavior which was returning an instructions count close to
> the number of cycles (CPI ~= 1).
>
> Signed-off-by: Clément Léger <cleger@rivosinc.com>

Thanks!

Applied to riscv-to-apply.next

Alistair

>
> ---
>  target/riscv/csr.c | 29 ++++++++++++++++-------------
>  1 file changed, 16 insertions(+), 13 deletions(-)
>
> diff --git a/target/riscv/csr.c b/target/riscv/csr.c
> index 726096444f..5f1dcee102 100644
> --- a/target/riscv/csr.c
> +++ b/target/riscv/csr.c
> @@ -762,14 +762,17 @@ static RISCVException write_vcsr(CPURISCVState *env, 
> int csrno,
>  }
>
>  /* User Timers and Counters */
> -static target_ulong get_ticks(bool shift)
> +static target_ulong get_ticks(bool shift, bool instructions)
>  {
>      int64_t val;
>      target_ulong result;
>
>  #if !defined(CONFIG_USER_ONLY)
>      if (icount_enabled()) {
> -        val = icount_get();
> +        if (instructions)
> +            val = icount_get_raw();
> +        else
> +            val = icount_get();
>      } else {
>          val = cpu_get_host_ticks();
>      }
> @@ -804,14 +807,14 @@ static RISCVException read_timeh(CPURISCVState *env, 
> int csrno,
>  static RISCVException read_hpmcounter(CPURISCVState *env, int csrno,
>                                        target_ulong *val)
>  {
> -    *val = get_ticks(false);
> +    *val = get_ticks(false, (csrno == CSR_INSTRET));
>      return RISCV_EXCP_NONE;
>  }
>
>  static RISCVException read_hpmcounterh(CPURISCVState *env, int csrno,
>                                         target_ulong *val)
>  {
> -    *val = get_ticks(true);
> +    *val = get_ticks(true, (csrno == CSR_INSTRETH));
>      return RISCV_EXCP_NONE;
>  }
>
> @@ -875,11 +878,11 @@ static RISCVException write_mhpmcounter(CPURISCVState 
> *env, int csrno,
>      int ctr_idx = csrno - CSR_MCYCLE;
>      PMUCTRState *counter = &env->pmu_ctrs[ctr_idx];
>      uint64_t mhpmctr_val = val;
> +    bool instr = riscv_pmu_ctr_monitor_instructions(env, ctr_idx);
>
>      counter->mhpmcounter_val = val;
> -    if (riscv_pmu_ctr_monitor_cycles(env, ctr_idx) ||
> -        riscv_pmu_ctr_monitor_instructions(env, ctr_idx)) {
> -        counter->mhpmcounter_prev = get_ticks(false);
> +    if (riscv_pmu_ctr_monitor_cycles(env, ctr_idx) || instr) {
> +        counter->mhpmcounter_prev = get_ticks(false, instr);
>          if (ctr_idx > 2) {
>              if (riscv_cpu_mxl(env) == MXL_RV32) {
>                  mhpmctr_val = mhpmctr_val |
> @@ -902,12 +905,12 @@ static RISCVException write_mhpmcounterh(CPURISCVState 
> *env, int csrno,
>      PMUCTRState *counter = &env->pmu_ctrs[ctr_idx];
>      uint64_t mhpmctr_val = counter->mhpmcounter_val;
>      uint64_t mhpmctrh_val = val;
> +    bool instr = riscv_pmu_ctr_monitor_instructions(env, ctr_idx);
>
>      counter->mhpmcounterh_val = val;
>      mhpmctr_val = mhpmctr_val | (mhpmctrh_val << 32);
> -    if (riscv_pmu_ctr_monitor_cycles(env, ctr_idx) ||
> -        riscv_pmu_ctr_monitor_instructions(env, ctr_idx)) {
> -        counter->mhpmcounterh_prev = get_ticks(true);
> +    if (riscv_pmu_ctr_monitor_cycles(env, ctr_idx) || instr) {
> +        counter->mhpmcounterh_prev = get_ticks(true, instr);
>          if (ctr_idx > 2) {
>              riscv_pmu_setup_timer(env, mhpmctr_val, ctr_idx);
>          }
> @@ -926,6 +929,7 @@ static RISCVException riscv_pmu_read_ctr(CPURISCVState 
> *env, target_ulong *val,
>                                           counter->mhpmcounter_prev;
>      target_ulong ctr_val = upper_half ? counter->mhpmcounterh_val :
>                                          counter->mhpmcounter_val;
> +    bool instr = riscv_pmu_ctr_monitor_instructions(env, ctr_idx);
>
>      if (get_field(env->mcountinhibit, BIT(ctr_idx))) {
>          /*
> @@ -946,9 +950,8 @@ static RISCVException riscv_pmu_read_ctr(CPURISCVState 
> *env, target_ulong *val,
>       * The kernel computes the perf delta by subtracting the current value 
> from
>       * the value it initialized previously (ctr_val).
>       */
> -    if (riscv_pmu_ctr_monitor_cycles(env, ctr_idx) ||
> -        riscv_pmu_ctr_monitor_instructions(env, ctr_idx)) {
> -        *val = get_ticks(upper_half) - ctr_prev + ctr_val;
> +    if (riscv_pmu_ctr_monitor_cycles(env, ctr_idx) || instr) {
> +        *val = get_ticks(upper_half, instr) - ctr_prev + ctr_val;
>      } else {
>          *val = ctr_val;
>      }
> --
> 2.43.0
>
>