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From: Alex =?utf-8?Q?Benn=C3=A9e?= <alex.bennee@linaro.org>
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Date: Wed, 12 Jul 2017 15:36:36 +0100
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Subject: Re: [Qemu-devel] [PATCH 04/22] tcg: fix corruption of code_time
 profiling counter upon tb_flush
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To: "Emilio G. Cota" <cota@braap.org>
Cc: qemu-devel@nongnu.org, Richard Henderson <rth@twiddle.net>


Emilio G. Cota <cota@braap.org> writes:

> Whenever there is an overflow in code_gen_buffer (e.g. we run out
> of space in it and have to flush it), the code_time profiling counter
> ends up with an invalid value (that is, code_time -= profile_getclock(),
> without later on getting += profile_getclock() due to the goto).
>
> Fix it by using the ti variable, so that we only update code_time
> when there is no overflow. Note that in case there is an overflow
> we fail to account for the elapsed coding time, but this is quite rare
> so we can probably live with it.
>
<snip>
>
> Signed-off-by: Emilio G. Cota <cota@braap.org>

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>

> ---
>  accel/tcg/translate-all.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/accel/tcg/translate-all.c b/accel/tcg/translate-all.c
> index a936a5f..72ce445 100644
> --- a/accel/tcg/translate-all.c
> +++ b/accel/tcg/translate-all.c
> @@ -1293,7 +1293,7 @@ TranslationBlock *tb_gen_code(CPUState *cpu,
>  #ifdef CONFIG_PROFILER
>      tcg_ctx.tb_count++;
>      tcg_ctx.interm_time += profile_getclock() - ti;
> -    tcg_ctx.code_time -= profile_getclock();
> +    ti = profile_getclock();
>  #endif
>
>      /* ??? Overflow could be handled better here.  In particular, we
> @@ -1311,7 +1311,7 @@ TranslationBlock *tb_gen_code(CPUState *cpu,
>      }
>
>  #ifdef CONFIG_PROFILER
> -    tcg_ctx.code_time += profile_getclock();
> +    tcg_ctx.code_time += profile_getclock() - ti;
>      tcg_ctx.code_in_len += tb->size;
>      tcg_ctx.code_out_len += gen_code_size;
>      tcg_ctx.search_out_len += search_size;


--
Alex Bennée