On 3/21/22 11:30, Tvrtko Ursulin wrote:
On 19/03/2022 19:42, 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.
And now we know, or we know it is not a concern?
To make i915 more architecture-neutral and be less paranoid, lets
attempt to
"Lets attempt" as we don't know if this will work and/or what can/will
break?
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@xxxxxxxxx>
---
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);
And as noticed before, drm_clfush_sg still can call wbinvd_on_all_cpus
so are you just punting the issue somewhere else? How will it be
solved there?
I think in this case, drm_clflush_sg() can't be immediately used,
because pages may not contain actual page pointers; might be just the
dma address. It needs to be preceded with a dmabuf vmap.
But otherwise this change, I figure, falls into the "prefer range-aware
apis" category; If the CPU supports it, flush the range only, otherwise
fall back to wbinvd().
/Thomas
Regards,
Tvrtko
sg_page_sizes = i915_sg_dma_sizes(pages->sgl);
__i915_gem_object_set_pages(obj, pages, sg_page_sizes);
