Re: [Qemu-devel] [PATCH 3/3] target-ppc: use separate indices for various translation modes

[Alexander Graf]

On 20.02.15 13:45, Paolo Bonzini wrote:
> PowerPC TCG flushes the TLB on every IR/DR change, which basically
> means on every user<->kernel context switch.  Encode IR/DR in the
> MMU index.
> 
> This brings the number of TLB flushes down from ~900000 to ~50000
> for starting up the Debian installer, which is in line with x86
> and gives a ~10% performance improvement.
> 
> Signed-off-by: Paolo Bonzini <address@hidden>
> ---
>  target-ppc/cpu.h         |  7 ++-----
>  target-ppc/excp_helper.c |  3 ---
>  target-ppc/helper_regs.h | 11 ++++++-----
>  3 files changed, 8 insertions(+), 13 deletions(-)
> 
> diff --git a/target-ppc/cpu.h b/target-ppc/cpu.h
> index aae33a9..610d884 100644
> --- a/target-ppc/cpu.h
> +++ b/target-ppc/cpu.h
> @@ -943,7 +943,8 @@ struct ppc_segment_page_sizes {
>  
>  
> /*****************************************************************************/
>  /* The whole PowerPC CPU context */
> -#define NB_MMU_MODES 3
> +#define NB_MMU_MODES 12
> +#define MMU_USER_IDX 3  /* PR=IR=DR=1 */
>  
>  #define PPC_CPU_OPCODES_LEN          0x40
>  #define PPC_CPU_INDIRECT_OPCODES_LEN 0x20
> @@ -1252,10 +1253,6 @@ static inline CPUPPCState *cpu_init(const char 
> *cpu_model)
>  #define cpu_list ppc_cpu_list
>  
>  /* MMU modes definitions */
> -#define MMU_MODE0_SUFFIX _user
> -#define MMU_MODE1_SUFFIX _kernel
> -#define MMU_MODE2_SUFFIX _hypv
> -#define MMU_USER_IDX 0
>  static inline int cpu_mmu_index (CPUPPCState *env)
>  {
>      return env->mmu_idx;
> diff --git a/target-ppc/excp_helper.c b/target-ppc/excp_helper.c
> index b803475..f608701 100644
> --- a/target-ppc/excp_helper.c
> +++ b/target-ppc/excp_helper.c
> @@ -623,9 +623,6 @@ static inline void powerpc_excp(PowerPCCPU *cpu, int 
> excp_model, int excp)
>  
>      if (env->spr[SPR_LPCR] & LPCR_AIL) {
>          new_msr |= (1 << MSR_IR) | (1 << MSR_DR);
> -    } else if (msr & ((1 << MSR_IR) | (1 << MSR_DR))) {
> -        /* If we disactivated any translation, flush TLBs */
> -        tlb_flush(cs, 1);
>      }
>  
>  #ifdef TARGET_PPC64
> diff --git a/target-ppc/helper_regs.h b/target-ppc/helper_regs.h
> index 271fddf..23b8ded 100644
> --- a/target-ppc/helper_regs.h
> +++ b/target-ppc/helper_regs.h
> @@ -41,12 +41,15 @@ static inline void hreg_swap_gpr_tgpr(CPUPPCState *env)
>  
>  static inline void hreg_compute_mem_idx(CPUPPCState *env)
>  {
> +    int high;
> +
>      /* Precompute MMU index */
>      if (msr_pr == 0 && msr_hv != 0) {
> -        env->mmu_idx = 2;
> +        high = 2;

Could you instead do something like

  uint32_t mmu_idx = 0;

  mmu_idx |= MMU_IDX_HV;

>      } else {
> -        env->mmu_idx = 1 - msr_pr;
> +        high = 1 - msr_pr;

  mmu_idx |= (msr_pr & 1) ? MMU_IDX_PR;

>      }
> +    env->mmu_idx = (high << 2) | (msr_ir << 1) | msr_dr;

  mmu_idx |= (msr_ir & 1) ? MMU_IDX_IR;
  mmu_idx |= (msr_dr & 1) ? MMU_IDX_DR;
  env->mmu_idx = mmu_idx;

and check whether the compiler is smart enough to optimize this out
considering that it's all constants?

Also please double-check that 440 still works. That was the target that
gave me the most headaches on DR/IR switching so far.

Otherwise looks simple and clean to me :).


Alex

>  }
>  
>  static inline void hreg_compute_hflags(CPUPPCState *env)
> @@ -56,7 +59,7 @@ static inline void hreg_compute_hflags(CPUPPCState *env)
>      /* We 'forget' FE0 & FE1: we'll never generate imprecise exceptions */
>      hflags_mask = (1 << MSR_VR) | (1 << MSR_AP) | (1 << MSR_SA) |
>          (1 << MSR_PR) | (1 << MSR_FP) | (1 << MSR_SE) | (1 << MSR_BE) |
> -        (1 << MSR_LE) | (1 << MSR_VSX);
> +        (1 << MSR_LE) | (1 << MSR_VSX) | (1 << MSR_IR) | (1 << MSR_DR);
>      hflags_mask |= (1ULL << MSR_CM) | (1ULL << MSR_SF) | MSR_HVB;
>      hreg_compute_mem_idx(env);
>      env->hflags = env->msr & hflags_mask;
> @@ -82,8 +85,6 @@ static inline int hreg_store_msr(CPUPPCState *env, 
> target_ulong value,
>      }
>      if (((value >> MSR_IR) & 1) != msr_ir ||
>          ((value >> MSR_DR) & 1) != msr_dr) {
> -        /* Flush all tlb when changing translation mode */
> -        tlb_flush(cs, 1);
>          excp = POWERPC_EXCP_NONE;
>          cs->interrupt_request |= CPU_INTERRUPT_EXITTB;
>      }
>