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

[Philippe Mathieu-Daudé]

On 5/6/23 23:56, BALATON Zoltan wrote:
> 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.

I tried that first but found it was not obvious, so chose this
form because it seemed clearer to me.