On Sun, Oct 18, 2015 at 02:07:13PM +0100, Chris Wilson wrote:
> > I couldn't spot the difference either. I am beginning to suspect it is
> > gcc as
> >
> > diff --git a/drivers/gpu/drm/drm_cache.c b/drivers/gpu/drm/drm_cache.c
> > index 6743ff7..c9097b5 100644
> > --- a/drivers/gpu/drm/drm_cache.c
> > +++ b/drivers/gpu/drm/drm_cache.c
> > @@ -130,11 +130,11 @@ drm_clflush_virt_range(void *addr, unsigned long length)
> > {
> > #if defined(CONFIG_X86)
> > if (cpu_has_clflush) {
> > const int size = boot_cpu_data.x86_clflush_size;
> > - void *end = addr + length;
> > + void *end = addr + length - 1;
> > addr = (void *)(((unsigned long)addr) & -size);
> > mb();
> > - for (; addr < end; addr += size)
> > + for (; addr <= end; addr += size)
> > clflushopt(addr);
> > mb();
> > return;
>
> s/clflushopt/clflush/ works just as well.
>
> Plot thickens. Current guess is that gcc doesn't see the constraints
> underneath the alternative()?
Adding a barrier() after clflushopt() in the loop is sufficient as well.
Almost certain that alternative() is confusing gcc.
-Chris
--
Chris Wilson, Intel Open Source Technology Centre
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