target/riscv: fix instructions count handling in icount mode

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>

Reviewed-by: Atish Patra <atishp@rivosinc.com>
Message-ID: <20240618112649.76683-1-cleger@rivosinc.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

1 files changed, 17 insertions, 13 deletions

diff --git a/target/riscv/csr.c b/target/riscv/csr.c
index 6f15612..432c59d 100644
--- a/target/riscv/csr.c
+++ b/target/riscv/csr.c
@@ -762,14 +762,18 @@ 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 +808,14 @@ 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 +879,11 @@ 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 +906,12 @@ 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 +930,7 @@ 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 +951,8 @@ 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;
     }