Re: [PATCH] drm/i915: Use memset64() to align the ring with MI_NOOP

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On 25/04/2018 15:09, Chris Wilson wrote:
Quoting Tvrtko Ursulin (2018-04-25 15:00:43)

On 25/04/2018 13:37, Chris Wilson wrote:
When filling the ring to align the emit pointer to the next cacheline,
use memset64() rather than open-coding it. As we know that we always
have an even number of dwords, we can replace the dword loop with the
qword equivalent.

Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
---
   drivers/gpu/drm/i915/intel_ringbuffer.c | 14 ++++++++------
   1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index c68ac605b8a9..07a9a2b4beb7 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -1717,22 +1717,24 @@ u32 *intel_ring_begin(struct i915_request *rq, unsigned int num_dwords)
   /* Align the ring tail to a cacheline boundary */
   int intel_ring_cacheline_align(struct i915_request *rq)
   {
-     int num_dwords = (rq->ring->emit & (CACHELINE_BYTES - 1)) / sizeof(u32);
-     u32 *cs;
+     int num_dwords;
+     void *cs;
+ num_dwords = (rq->ring->emit & (CACHELINE_BYTES - 1)) / sizeof(u32);
       if (num_dwords == 0)
               return 0;
- num_dwords = CACHELINE_BYTES / sizeof(u32) - num_dwords;
+     num_dwords = CACHELINE_DWORDS - num_dwords;
+     GEM_BUG_ON(num_dwords & 1);
+
       cs = intel_ring_begin(rq, num_dwords);
       if (IS_ERR(cs))
               return PTR_ERR(cs);
- while (num_dwords--)
-             *cs++ = MI_NOOP;
-

BUILD_BUG_ON(MI_NOOP != 0) for paranoid future proofing, since MI_NOOP
is now not mentioned in this function, but is meant.

((u64)MI_NOOP << 32 | MI_NOOP) ?

That also works, can keep the r-b.

Regards,

Tvrtko
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