Re: [PATCH v9 06/10] target/ppc: enable PMU instruction count

[David Gibson]

On Wed, Dec 01, 2021 at 12:17:30PM -0300, Daniel Henrique Barboza wrote:
> The PMU is already counting cycles by calculating time elapsed in
> nanoseconds. Counting instructions is a different matter and requires
> another approach.
> 
> This patch adds the capability of counting completed instructions (Perf
> event PM_INST_CMPL) by counting the amount of instructions translated in
> each translation block right before exiting it.
> 
> A new pmu_count_insns() helper in translation.c was added to do that.
> After verifying that the PMU is counting instructions, call
> helper_insns_inc(). This new helper from power8-pmu.c will add the
> instructions to the relevant counters. It'll also be responsible for
> triggering counter negative overflows as it is already being done with
> cycles.
> 
> To verify whether the PMU is counting instructions or now, a new hflags
> named 'HFLAGS_INSN_CNT' is introduced. This flag will match the internal
> state of the PMU. We're be using this flag to avoid calling
> helper_insn_inc() when we do not have a valid instruction event being
> sampled.
> 
> Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

> ---
>  target/ppc/cpu.h                 |  1 +
>  target/ppc/helper.h              |  1 +
>  target/ppc/helper_regs.c         |  7 ++++
>  target/ppc/power8-pmu-regs.c.inc |  6 +++
>  target/ppc/power8-pmu.c          | 67 +++++++++++++++++++++++++++++++-
>  target/ppc/power8-pmu.h          |  1 +
>  target/ppc/translate.c           | 64 ++++++++++++++++++++++++++++++
>  7 files changed, 146 insertions(+), 1 deletion(-)
> 
> diff --git a/target/ppc/cpu.h b/target/ppc/cpu.h
> index f562d5b933..28a185fb25 100644
> --- a/target/ppc/cpu.h
> +++ b/target/ppc/cpu.h
> @@ -655,6 +655,7 @@ enum {
>      HFLAGS_PR = 14,  /* MSR_PR */
>      HFLAGS_PMCC0 = 15,  /* MMCR0 PMCC bit 0 */
>      HFLAGS_PMCC1 = 16,  /* MMCR0 PMCC bit 1 */
> +    HFLAGS_INSN_CNT = 17, /* PMU instruction count enabled */
>      HFLAGS_VSX = 23, /* MSR_VSX if cpu has VSX */
>      HFLAGS_VR = 25,  /* MSR_VR if cpu has VRE */
>  
> diff --git a/target/ppc/helper.h b/target/ppc/helper.h
> index 94b4690375..d8a23e054a 100644
> --- a/target/ppc/helper.h
> +++ b/target/ppc/helper.h
> @@ -24,6 +24,7 @@ DEF_HELPER_2(store_mmcr0, void, env, tl)
>  DEF_HELPER_2(store_mmcr1, void, env, tl)
>  DEF_HELPER_3(store_pmc, void, env, i32, i64)
>  DEF_HELPER_2(read_pmc, tl, env, i32)
> +DEF_HELPER_2(insns_inc, void, env, i32)
>  #endif
>  DEF_HELPER_1(check_tlb_flush_local, void, env)
>  DEF_HELPER_1(check_tlb_flush_global, void, env)
> diff --git a/target/ppc/helper_regs.c b/target/ppc/helper_regs.c
> index 99562edd57..b847928842 100644
> --- a/target/ppc/helper_regs.c
> +++ b/target/ppc/helper_regs.c
> @@ -23,6 +23,7 @@
>  #include "exec/exec-all.h"
>  #include "sysemu/kvm.h"
>  #include "helper_regs.h"
> +#include "power8-pmu.h"
>  
>  /* Swap temporary saved registers with GPRs */
>  void hreg_swap_gpr_tgpr(CPUPPCState *env)
> @@ -121,6 +122,12 @@ static uint32_t hreg_compute_hflags_value(CPUPPCState 
> *env)
>          hflags |= 1 << HFLAGS_HV;
>      }
>  
> +#if defined(TARGET_PPC64)
> +    if (pmu_insn_cnt_enabled(env)) {
> +        hflags |= 1 << HFLAGS_INSN_CNT;
> +    }
> +#endif
> +
>      /*
>       * This is our encoding for server processors. The architecture
>       * specifies that there is no such thing as userspace with
> diff --git a/target/ppc/power8-pmu-regs.c.inc 
> b/target/ppc/power8-pmu-regs.c.inc
> index 25b13ad564..2bab6cece7 100644
> --- a/target/ppc/power8-pmu-regs.c.inc
> +++ b/target/ppc/power8-pmu-regs.c.inc
> @@ -113,6 +113,12 @@ static void write_MMCR0_common(DisasContext *ctx, TCGv 
> val)
>       */
>      gen_icount_io_start(ctx);
>      gen_helper_store_mmcr0(cpu_env, val);
> +
> +    /*
> +     * End the translation block because MMCR0 writes can change
> +     * ctx->pmu_insn_cnt.
> +     */
> +    ctx->base.is_jmp = DISAS_EXIT_UPDATE;
>  }
>  
>  void spr_write_MMCR0_ureg(DisasContext *ctx, int sprn, int gprn)
> diff --git a/target/ppc/power8-pmu.c b/target/ppc/power8-pmu.c
> index 399234a2fc..e163ba5640 100644
> --- a/target/ppc/power8-pmu.c
> +++ b/target/ppc/power8-pmu.c
> @@ -112,6 +112,54 @@ static PMUEventType pmc_get_event(CPUPPCState *env, int 
> sprn)
>      return evt_type;
>  }
>  
> +bool pmu_insn_cnt_enabled(CPUPPCState *env)
> +{
> +    int sprn;
> +
> +    for (sprn = SPR_POWER_PMC1; sprn <= SPR_POWER_PMC5; sprn++) {
> +        if (pmc_get_event(env, sprn) == PMU_EVENT_INSTRUCTIONS) {
> +            return true;
> +        }
> +    }
> +
> +    return false;
> +}
> +
> +static bool pmu_increment_insns(CPUPPCState *env, uint32_t num_insns)
> +{
> +    bool overflow_triggered = false;
> +    int sprn;
> +
> +    /* PMC6 never counts instructions */
> +    for (sprn = SPR_POWER_PMC1; sprn <= SPR_POWER_PMC5; sprn++) {
> +        if (pmc_get_event(env, sprn) != PMU_EVENT_INSTRUCTIONS) {
> +            continue;
> +        }
> +
> +        env->spr[sprn] += num_insns;
> +
> +        if (env->spr[sprn] >= PMC_COUNTER_NEGATIVE_VAL &&
> +            pmc_has_overflow_enabled(env, sprn)) {
> +
> +            overflow_triggered = true;
> +
> +            /*
> +             * The real PMU will always trigger a counter overflow with
> +             * PMC_COUNTER_NEGATIVE_VAL. We don't have an easy way to
> +             * do that since we're counting block of instructions at
> +             * the end of each translation block, and we're probably
> +             * passing this value at this point.
> +             *
> +             * Let's write PMC_COUNTER_NEGATIVE_VAL to the overflowed
> +             * counter to simulate what the real hardware would do.
> +             */
> +            env->spr[sprn] = PMC_COUNTER_NEGATIVE_VAL;
> +        }
> +    }
> +
> +    return overflow_triggered;
> +}
> +
>  static void pmu_update_cycles(CPUPPCState *env)
>  {
>      uint64_t now = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
> @@ -195,7 +243,7 @@ void helper_store_mmcr0(CPUPPCState *env, target_ulong 
> value)
>  
>      env->spr[SPR_POWER_MMCR0] = value;
>  
> -    /* MMCR0 writes can change HFLAGS_PMCCCLEAR */
> +    /* MMCR0 writes can change HFLAGS_PMCCCLEAR and HFLAGS_INSN_CNT */
>      hreg_compute_hflags(env);
>  
>      /* Update cycle overflow timers with the current MMCR0 state */
> @@ -207,6 +255,9 @@ void helper_store_mmcr1(CPUPPCState *env, uint64_t value)
>      pmu_update_cycles(env);
>  
>      env->spr[SPR_POWER_MMCR1] = value;
> +
> +    /* MMCR1 writes can change HFLAGS_INSN_CNT */
> +    hreg_compute_hflags(env);
>  }
>  
>  target_ulong helper_read_pmc(CPUPPCState *env, uint32_t sprn)
> @@ -237,6 +288,20 @@ static void fire_PMC_interrupt(PowerPCCPU *cpu)
>      return;
>  }
>  
> +/* This helper assumes that the PMC is running. */
> +void helper_insns_inc(CPUPPCState *env, uint32_t num_insns)
> +{
> +    bool overflow_triggered;
> +    PowerPCCPU *cpu;
> +
> +    overflow_triggered = pmu_increment_insns(env, num_insns);
> +
> +    if (overflow_triggered) {
> +        cpu = env_archcpu(env);
> +        fire_PMC_interrupt(cpu);
> +    }
> +}
> +
>  static void cpu_ppc_pmu_timer_cb(void *opaque)
>  {
>      PowerPCCPU *cpu = opaque;
> diff --git a/target/ppc/power8-pmu.h b/target/ppc/power8-pmu.h
> index 49a813a443..3ee4b4cda5 100644
> --- a/target/ppc/power8-pmu.h
> +++ b/target/ppc/power8-pmu.h
> @@ -21,5 +21,6 @@
>  #include "qemu/main-loop.h"
>  
>  void cpu_ppc_pmu_init(CPUPPCState *env);
> +bool pmu_insn_cnt_enabled(CPUPPCState *env);
>  
>  #endif
> diff --git a/target/ppc/translate.c b/target/ppc/translate.c
> index 9960df6e18..896b916021 100644
> --- a/target/ppc/translate.c
> +++ b/target/ppc/translate.c
> @@ -177,6 +177,7 @@ struct DisasContext {
>      bool hr;
>      bool mmcr0_pmcc0;
>      bool mmcr0_pmcc1;
> +    bool pmu_insn_cnt;
>      ppc_spr_t *spr_cb; /* Needed to check rights for mfspr/mtspr */
>      int singlestep_enabled;
>      uint32_t flags;
> @@ -4170,6 +4171,49 @@ static inline void gen_update_cfar(DisasContext *ctx, 
> target_ulong nip)
>  #endif
>  }
>  
> +#if defined(TARGET_PPC64)
> +static void pmu_count_insns(DisasContext *ctx)
> +{
> +    /*
> +     * Do not bother calling the helper if the PMU isn't counting
> +     * instructions.
> +     */
> +    if (!ctx->pmu_insn_cnt) {
> +        return;
> +    }
> +
> + #if !defined(CONFIG_USER_ONLY)
> +    /*
> +     * The PMU insns_inc() helper stops the internal PMU timer if a
> +     * counter overflows happens. In that case, if the guest is
> +     * running with icount and we do not handle it beforehand,
> +     * the helper can trigger a 'bad icount read'.
> +     */
> +    gen_icount_io_start(ctx);
> +
> +    gen_helper_insns_inc(cpu_env, tcg_constant_i32(ctx->base.num_insns));
> +#else
> +    /*
> +     * User mode can read (but not write) PMC5 and start/stop
> +     * the PMU via MMCR0_FC. In this case just increment
> +     * PMC5 with base.num_insns.
> +     */
> +    TCGv t0 = tcg_temp_new();
> +
> +    gen_load_spr(t0, SPR_POWER_PMC5);
> +    tcg_gen_addi_tl(t0, t0, ctx->base.num_insns);
> +    gen_store_spr(SPR_POWER_PMC5, t0);
> +
> +    tcg_temp_free(t0);
> +#endif /* #if !defined(CONFIG_USER_ONLY) */
> +}
> +#else
> +static void pmu_count_insns(DisasContext *ctx)
> +{
> +    return;
> +}
> +#endif /* #if defined(TARGET_PPC64) */
> +
>  static inline bool use_goto_tb(DisasContext *ctx, target_ulong dest)
>  {
>      return translator_use_goto_tb(&ctx->base, dest);
> @@ -4180,6 +4224,14 @@ static void gen_lookup_and_goto_ptr(DisasContext *ctx)
>      if (unlikely(ctx->singlestep_enabled)) {
>          gen_debug_exception(ctx);
>      } else {
> +        /*
> +         * tcg_gen_lookup_and_goto_ptr will exit the TB if
> +         * CF_NO_GOTO_PTR is set. Count insns now.
> +         */
> +        if (ctx->base.tb->flags & CF_NO_GOTO_PTR) {
> +            pmu_count_insns(ctx);
> +        }
> +
>          tcg_gen_lookup_and_goto_ptr();
>      }
>  }
> @@ -4191,6 +4243,7 @@ static void gen_goto_tb(DisasContext *ctx, int n, 
> target_ulong dest)
>          dest = (uint32_t) dest;
>      }
>      if (use_goto_tb(ctx, dest)) {
> +        pmu_count_insns(ctx);
>          tcg_gen_goto_tb(n);
>          tcg_gen_movi_tl(cpu_nip, dest & ~3);
>          tcg_gen_exit_tb(ctx->base.tb, n);
> @@ -8458,6 +8511,7 @@ static void ppc_tr_init_disas_context(DisasContextBase 
> *dcbase, CPUState *cs)
>      ctx->hr = (hflags >> HFLAGS_HR) & 1;
>      ctx->mmcr0_pmcc0 = (hflags >> HFLAGS_PMCC0) & 1;
>      ctx->mmcr0_pmcc1 = (hflags >> HFLAGS_PMCC1) & 1;
> +    ctx->pmu_insn_cnt = (hflags >> HFLAGS_INSN_CNT) & 1;
>  
>      ctx->singlestep_enabled = 0;
>      if ((hflags >> HFLAGS_SE) & 1) {
> @@ -8564,6 +8618,7 @@ static void ppc_tr_tb_stop(DisasContextBase *dcbase, 
> CPUState *cs)
>      switch (is_jmp) {
>      case DISAS_TOO_MANY:
>          if (use_goto_tb(ctx, nip)) {
> +            pmu_count_insns(ctx);
>              tcg_gen_goto_tb(0);
>              gen_update_nip(ctx, nip);
>              tcg_gen_exit_tb(ctx->base.tb, 0);
> @@ -8574,6 +8629,14 @@ static void ppc_tr_tb_stop(DisasContextBase *dcbase, 
> CPUState *cs)
>          gen_update_nip(ctx, nip);
>          /* fall through */
>      case DISAS_CHAIN:
> +        /*
> +         * tcg_gen_lookup_and_goto_ptr will exit the TB if
> +         * CF_NO_GOTO_PTR is set. Count insns now.
> +         */
> +        if (ctx->base.tb->flags & CF_NO_GOTO_PTR) {
> +            pmu_count_insns(ctx);
> +        }
> +
>          tcg_gen_lookup_and_goto_ptr();
>          break;
>  
> @@ -8581,6 +8644,7 @@ static void ppc_tr_tb_stop(DisasContextBase *dcbase, 
> CPUState *cs)
>          gen_update_nip(ctx, nip);
>          /* fall through */
>      case DISAS_EXIT:
> +        pmu_count_insns(ctx);
>          tcg_gen_exit_tb(NULL, 0);
>          break;
>  

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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