Re: [PATCH v4 20/61] drm/i915: Rework clflush to work correctly without obj->mm.lock.

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On 11/2/20 10:22 AM, Thomas Hellström wrote:

On 11/2/20 9:48 AM, Maarten Lankhorst wrote:
Op 30-10-2020 om 16:08 schreef Thomas Hellström:
On 10/16/20 12:44 PM, Maarten Lankhorst wrote:
Pin in the caller, not in the work itself. This should also
work better for dma-fence annotations.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
---
   drivers/gpu/drm/i915/gem/i915_gem_clflush.c | 15 +++++++--------
   1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_clflush.c b/drivers/gpu/drm/i915/gem/i915_gem_clflush.c
index bc0223716906..daf9284ef1f5 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_clflush.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_clflush.c
@@ -27,15 +27,8 @@ static void __do_clflush(struct drm_i915_gem_object *obj)
   static int clflush_work(struct dma_fence_work *base)
   {
       struct clflush *clflush = container_of(base, typeof(*clflush), base);
-    struct drm_i915_gem_object *obj = clflush->obj;
-    int err;
   -    err = i915_gem_object_pin_pages(obj);
-    if (err)
-        return err;
-
-    __do_clflush(obj);
-    i915_gem_object_unpin_pages(obj);
+    __do_clflush(clflush->obj);
         return 0;
   }
@@ -44,6 +37,7 @@ static void clflush_release(struct dma_fence_work *base)
   {
       struct clflush *clflush = container_of(base, typeof(*clflush), base);
   +    i915_gem_object_unpin_pages(clflush->obj);
Hmm, Could we do without pinning here? Pages present are protected first by the object lock, then by the fence?

/Thomas



I felt the least chance of regressions was to copy the existing code. :)

At least until we have completed obj->mm.lock removal, we shouldn't try to be smart with these kind of things.

Likely, we've already pinned the pages, so it's a simple ref increase.

Later on, we can try to be smart, but whenever I tried to change behavior so far, I was forced to hunt down bugs.

OK, sounds good.

Reviewed-by: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>


/Thomas




~Maarten

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