Re: [Qemu-devel] [PATCH v1 2/3] tcg-runtime: light re-factor of lookup_tb_ptr

[Pranith Kumar]

Hi Alex,

On Wed, Jun 14, 2017 at 10:02 AM, Alex Bennée <address@hidden> wrote:
> Just a little precursor re-factoring before I was going to add a trace
> point:
>
>   - single return point, defaulting to tcg_ctx.code_gen_epilogue
>   - move cs_base, pc and flags inside the jump cache hit scope
>   - calculate the tb_jmp_cache hash once
>
> Signed-off-by: Alex Bennée <address@hidden>
> ---
>  tcg-runtime.c | 35 +++++++++++++++++++----------------
>  1 file changed, 19 insertions(+), 16 deletions(-)

Phew, glad you got this figured out! I tested it on the images I have
and it works. Please add:

Tested-by: Pranith Kumar <address@hidden>


>
> diff --git a/tcg-runtime.c b/tcg-runtime.c
> index 7fa90ce508..f4bfa9cea6 100644
> --- a/tcg-runtime.c
> +++ b/tcg-runtime.c
> @@ -147,30 +147,33 @@ uint64_t HELPER(ctpop_i64)(uint64_t arg)
>  void *HELPER(lookup_tb_ptr)(CPUArchState *env, target_ulong addr)
>  {
>      CPUState *cpu = ENV_GET_CPU(env);
> +    unsigned int addr_hash = tb_jmp_cache_hash_func(addr);
> +    void *code_ptr = NULL;
>      TranslationBlock *tb;
> -    target_ulong cs_base, pc;
> -    uint32_t flags;
>
> -    tb = atomic_rcu_read(&cpu->tb_jmp_cache[tb_jmp_cache_hash_func(addr)]);
> +    tb = atomic_rcu_read(&cpu->tb_jmp_cache[addr_hash]);
>      if (likely(tb)) {
> +        target_ulong cs_base, pc;
> +        uint32_t flags;
> +
>          cpu_get_tb_cpu_state(env, &pc, &cs_base, &flags);
> +
>          if (likely(tb->pc == addr && tb->cs_base == cs_base &&
>                     tb->flags == flags)) {
> -            goto found;
> -        }
> -        tb = tb_htable_lookup(cpu, addr, cs_base, flags);
> -        if (likely(tb)) {
> -            atomic_set(&cpu->tb_jmp_cache[tb_jmp_cache_hash_func(addr)], tb);
> -            goto found;
> +            code_ptr = tb->tc_ptr;
> +        } else {
> +            /* If we didn't find it in the jmp_cache we still might
> +             * find it in the global tb_htable
> +             */
> +            tb = tb_htable_lookup(cpu, addr, cs_base, flags);
> +            if (likely(tb)) {
> +                atomic_set(&cpu->tb_jmp_cache[addr_hash], tb);
> +                code_ptr = tb->tc_ptr;
> +            }
>          }
>      }
> -    return tcg_ctx.code_gen_epilogue;
> - found:
> -    qemu_log_mask_and_addr(CPU_LOG_EXEC, addr,
> -                           "Chain %p [%d: " TARGET_FMT_lx "] %s\n",
> -                           tb->tc_ptr, cpu->cpu_index, addr,
> -                           lookup_symbol(addr));
> -    return tb->tc_ptr;
> +
> +    return code_ptr ? code_ptr : tcg_ctx.code_gen_epilogue;
>  }
>
>  void HELPER(exit_atomic)(CPUArchState *env)
> --
> 2.13.0
>
>