Re: [Qemu-devel] [PATCH, RFT] Speedup 'tb_find_slow' by using the same heuristic as during memory page lookup

[Riku Voipio <riku.voipio@iki.fi>]

Hi,

tested and improves indeed startup speed.

On Mon, Nov 22, 2010 at 10:42:10PM +0300, Kirill Batuzov wrote:
> Move the last found TB to the head of the list so it will be found more  
> quickly next time it will be looked for.
>
> Signed-off-by: Kirill Batuzov <batuzovk@ispras.ru>
> Signed-off-by: Pavel Yushchenko <pau@ispras.ru>
> ---
> Hello.  This patch gives significant boost to a used by us rather rich  
> (for embedded one - featuring X-server, many daemons and applications)  
> ARM-based system literally decreasing its boot to desktop time by TWO  
> times!  (Average number of traversed 'tb_phys_hash' entries in the main  
> loop of the 'tb_find_slow' function reduced from 20 to 1.5.)  We were  
> able to shorten boot to login time by about 25% as well using Debian on  
> versatilepb (no X-server, only basic system). Seems like kernel booting  
> time is not affected.  No problems were encountered during our 
> experiments.
>
> We are looking forward for comments about this change and help with  
> testing. Thanks in advance!
>
>  cpu-exec.c |    5 +++++
>  1 files changed, 5 insertions(+), 0 deletions(-)
>
> diff --git a/cpu-exec.c b/cpu-exec.c
> index 5d6dd51..55c4526 100644
> --- a/cpu-exec.c
> +++ b/cpu-exec.c
> @@ -161,6 +161,11 @@ static TranslationBlock *tb_find_slow(target_ulong pc,
>      tb = tb_gen_code(env, pc, cs_base, flags, 0);
>
>   found:
> +    if (*ptb1) {
> +        *ptb1 = tb->phys_hash_next;
> +        tb->phys_hash_next = tb_phys_hash[h];
> +        tb_phys_hash[h] = tb;
> +    }
>      /* we add the TB in the virtual pc hash table */
>      env->tb_jmp_cache[tb_jmp_cache_hash_func(pc)] = tb;
>      return tb;