Re: [PATCH] util/cacheflush: Avoid flushing dcache twice when not necessary

[BALATON Zoltan]

On Mon, 5 Jun 2023, Philippe Mathieu-Daudé wrote:
> <libkern/OSCacheControl.h> describes sys_icache_invalidate() as
> "equivalent to sys_cache_control(kCacheFunctionPrepareForExecution)",
> having kCacheFunctionPrepareForExecution defined as:
>
>  /* Prepare memory for execution.  This should be called
>   * after writing machine instructions to memory, before
>   * executing them.  It syncs the dcache and icache. [...]
>   */
>
> Since the dcache is also sync'd, we can avoid the sys_dcache_flush()
> call when both rx/rw pointers are equal.
>
> Suggested-by: Richard Henderson <richard.henderson@linaro.org>
> Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> ---
> Based-on: <20230605175647.88395-2-philmd@linaro.org>
> ---
> util/cacheflush.c | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/util/cacheflush.c b/util/cacheflush.c
> index de35616718..a08906155a 100644
> --- a/util/cacheflush.c
> +++ b/util/cacheflush.c
> @@ -241,7 +241,14 @@ static void __attribute__((constructor)) 
> init_cache_info(void)
>
> void flush_idcache_range(uintptr_t rx, uintptr_t rw, size_t len)
> {
> -    sys_dcache_flush((void *)rw, len);
> +    if (rx == rw) {

Isn't it more straight forward to use rx != rw and drop the else branch 
than having an empty if branch? You can still keep the comment above the 
if to explain it if needed.

Regards,
BALATON Zoltan

> +        /*
> +         * sys_icache_invalidate() syncs the dcache and icache,
> +         * so no need to call sys_dcache_flush().
> +         */
> +    } else {
> +        sys_dcache_flush((void *)rw, len);
> +    }
>     sys_icache_invalidate((void *)rx, len);
> }
> #else