Re: [PATCH rdma-core 5/5] mlx5: Add support for ibv_alloc_null_mr

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On 6/20/2018 10:35 PM, Jason Gunthorpe wrote:
On Wed, Jun 20, 2018 at 07:28:22PM +0300, Yishai Hadas wrote:
@@ -80,7 +80,16 @@ static int copy_to_scat(struct mlx5_wqe_data_seg *scat, void *buf, int *size,
for (i = 0; i < max; ++i) {
  		copy = min_t(long, *size, be32toh(scat->byte_count));
-		memcpy((void *)(unsigned long)be64toh(scat->addr), buf, copy);
+
+		/* When NULL MR is used can't copy to target,
+		 * expected to be NULL.
+		 */
+		if (unlikely(scat->lkey == ctx->dump_fill_mkey_be))
+			;
+		else

What is that? Better as:

if (likely(scat->lkey != ctx->dump_fill_mkey_be))
			memcpy((void *)(unsigned long)be64toh(scat->addr),
			       buf, copy);


This is data path flow, upon performance testing we found the unlikely variant to be better than this suggestion.

I have updated the PR to handle other notes that you posted, please have a look.

Yishai

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