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

[Philippe Mathieu-Daudé]

Subject: "Avoid flushing dcache twice [on Darwin] when not necessary"

On 5/6/23 21:59, 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) {
> +        /*
> +         * 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