Re: [Qemu-devel] [RFC PATCH] tcg/softmmu: Increase size of TLB cache

[Richard Henderson]

On 07/24/2017 02:03 PM, Pranith Kumar wrote:
>   
> +#ifndef CPU_TLB_BITS_MAX
> +# define CPU_TLB_BITS_MAX 8

You should simply require each backend to define this.

> +++ b/tcg/i386/tcg-target.h
> @@ -162,6 +162,8 @@ extern bool have_popcnt;
>  # define TCG_AREG0 TCG_REG_EBP
>  #endif
>  
> +#define CPU_TLB_BITS_MAX 12

This is probably too much.

Exemplars:
NB_MMU_MODES = 1        moxie
NB_MMU_MODES = 2        m68k
NB_MMU_MODES = 3        alpha
NB_MMU_MODES = 7        arm
NB_MMU_MODES = 8        ppc64

sizeof(CPUArchState):

  tlb bits \ modes      1       2       3       7       8
        8               13856   25840   38952   92024   182576
        12              198176  394480  591912  1382264 1657136

Having 1.5MB of TLB data seems excessive.

Please let's get some performance numbers for various tlb bit sizes.

How much improvement do you get if you increase the size of the victim tlb 
cache?


r~