[Intel-gfx] [PATCH v2 1/1] i915/gem: drop wbinvd_on_all_cpus usage

[Lucas De Marchi]

On Thu, Apr 14, 2022 at 11:19:23AM -0700, Michael Cheng wrote:
>Previous concern with using drm_clflush_sg was that we don't know what the
>sg_table is pointing to, thus the usage of wbinvd_on_all_cpus to flush
>everything at once to avoid paranoia.

humn... and now we know it is backed by struct pages? I'm not sure I
follow what we didn't know before and now we do.

Thomas / Matthew, could you take another look herer if it seems correct
to you.


thanks
Lucas De Marchi


>To make i915 more architecture-neutral and be less paranoid, lets attempt to
>use drm_clflush_sg to flush the pages for when the GPU wants to read
>from main memory.
>
>Signed-off-by: Michael Cheng <michael.cheng at intel.com>
>---
> drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c | 9 ++-------
> 1 file changed, 2 insertions(+), 7 deletions(-)
>
>diff --git a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
>index f5062d0c6333..b0a5baaebc43 100644
>--- a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
>+++ b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
>@@ -8,6 +8,7 @@
> #include <linux/highmem.h>
> #include <linux/dma-resv.h>
> #include <linux/module.h>
>+#include <drm/drm_cache.h>
>
> #include <asm/smp.h>
>
>@@ -250,16 +251,10 @@ static int i915_gem_object_get_pages_dmabuf(struct drm_i915_gem_object *obj)
> 	 * DG1 is special here since it still snoops transactions even with
> 	 * CACHE_NONE. This is not the case with other HAS_SNOOP platforms. We
> 	 * might need to revisit this as we add new discrete platforms.
>-	 *
>-	 * XXX: Consider doing a vmap flush or something, where possible.
>-	 * Currently we just do a heavy handed wbinvd_on_all_cpus() here since
>-	 * the underlying sg_table might not even point to struct pages, so we
>-	 * can't just call drm_clflush_sg or similar, like we do elsewhere in
>-	 * the driver.
> 	 */
> 	if (i915_gem_object_can_bypass_llc(obj) ||
> 	    (!HAS_LLC(i915) && !IS_DG1(i915)))
>-		wbinvd_on_all_cpus();
>+		drm_clflush_sg(pages);
>
> 	sg_page_sizes = i915_sg_dma_sizes(pages->sgl);
> 	__i915_gem_object_set_pages(obj, pages, sg_page_sizes);
>-- 
>2.25.1
>