Re: [Qemu-devel] [PATCH v4 60/69] target/arm: Split gen_nop_hint

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 9/4/19 9:30 PM, Richard Henderson wrote:
> Now that all callers pass a constant value, split the switch
> statement into the individual trans_* functions.
> 
> Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  target/arm/translate.c | 67 +++++++++++++++---------------------------
>  1 file changed, 24 insertions(+), 43 deletions(-)
> 
> diff --git a/target/arm/translate.c b/target/arm/translate.c
> index 69092c12c3..d076c962ea 100644
> --- a/target/arm/translate.c
> +++ b/target/arm/translate.c
> @@ -3061,46 +3061,6 @@ static void gen_exception_return(DisasContext *s, TCGv_i32 pc)
>      gen_rfe(s, pc, load_cpu_field(spsr));
>  }
>  
> -/*
> - * For WFI we will halt the vCPU until an IRQ. For WFE and YIELD we
> - * only call the helper when running single threaded TCG code to ensure
> - * the next round-robin scheduled vCPU gets a crack. In MTTCG mode we
> - * just skip this instruction. Currently the SEV/SEVL instructions
> - * which are *one* of many ways to wake the CPU from WFE are not
> - * implemented so we can't sleep like WFI does.
> - */
> -static void gen_nop_hint(DisasContext *s, int val)
> -{
> -    switch (val) {
> -        /* When running in MTTCG we don't generate jumps to the yield and
> -         * WFE helpers as it won't affect the scheduling of other vCPUs.
> -         * If we wanted to more completely model WFE/SEV so we don't busy
> -         * spin unnecessarily we would need to do something more involved.
> -         */
> -    case 1: /* yield */
> -        if (!(tb_cflags(s->base.tb) & CF_PARALLEL)) {
> -            gen_set_pc_im(s, s->base.pc_next);
> -            s->base.is_jmp = DISAS_YIELD;
> -        }
> -        break;
> -    case 3: /* wfi */
> -        gen_set_pc_im(s, s->base.pc_next);
> -        s->base.is_jmp = DISAS_WFI;
> -        break;
> -    case 2: /* wfe */
> -        if (!(tb_cflags(s->base.tb) & CF_PARALLEL)) {
> -            gen_set_pc_im(s, s->base.pc_next);
> -            s->base.is_jmp = DISAS_WFE;
> -        }
> -        break;
> -    case 4: /* sev */
> -    case 5: /* sevl */
> -        /* TODO: Implement SEV, SEVL and WFE.  May help SMP performance.  */
> -    default: /* nop */
> -        break;
> -    }
> -}
> -
>  #define CPU_V001 cpu_V0, cpu_V0, cpu_V1
>  
>  static inline void gen_neon_add(int size, TCGv_i32 t0, TCGv_i32 t1)
> @@ -8194,19 +8154,40 @@ DO_SMLAWX(SMLAWT, 1, 1)
>  
>  static bool trans_YIELD(DisasContext *s, arg_YIELD *a)
>  {
> -    gen_nop_hint(s, 1);
> +    /*
> +     * When running single-threaded TCG code, use the helper to ensure that
> +     * the next round-robin scheduled vCPU gets a crack.  When running in
> +     * MTTCG we don't generate jumps to the helper as it won't affect the
> +     * scheduling of other vCPUs.
> +     */
> +    if (!(tb_cflags(s->base.tb) & CF_PARALLEL)) {
> +        gen_set_pc_im(s, s->base.pc_next);
> +        s->base.is_jmp = DISAS_YIELD;
> +    }
>      return true;
>  }
>  
>  static bool trans_WFE(DisasContext *s, arg_WFE *a)
>  {
> -    gen_nop_hint(s, 2);
> +    /*
> +     * When running single-threaded TCG code, use the helper to ensure that
> +     * the next round-robin scheduled vCPU gets a crack.  In MTTCG mode we
> +     * just skip this instruction.  Currently the SEV/SEVL instructions,
> +     * which are *one* of many ways to wake the CPU from WFE, are not
> +     * implemented so we can't sleep like WFI does.
> +     */
> +    if (!(tb_cflags(s->base.tb) & CF_PARALLEL)) {
> +        gen_set_pc_im(s, s->base.pc_next);
> +        s->base.is_jmp = DISAS_WFE;
> +    }
>      return true;
>  }
>  
>  static bool trans_WFI(DisasContext *s, arg_WFI *a)
>  {
> -    gen_nop_hint(s, 3);
> +    /* For WFI, halt the vCPU until an IRQ. */
> +    gen_set_pc_im(s, s->base.pc_next);
> +    s->base.is_jmp = DISAS_WFI;
>      return true;
>  }

Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>