Re: [PATCH] sbitmap: don't loop for find_next_zero_bit() for !round_robin

On 11/29/18 12:42 PM, Omar Sandoval wrote:

On Thu, Nov 29, 2018 at 12:34:12PM -0700, Jens Axboe wrote:

quoted

If we aren't forced to do round robin tag allocation, just use the
allocation hint to find the index for the tag word, don't use it for the
offset inside the word.

Maybe also add "We're already fetching that cache line, so we might as
well check the whole word."

Sure, will add.

quoted

@@ -130,12 +139,8 @@ int sbitmap_get(struct sbitmap *sb, unsigned int alloc_hint, bool round_robin)
 
 		/* Jump to next index. */
 		index++;
-		alloc_hint = index << sb->shift;
-
-		if (index >= sb->map_nr) {
+		if (index >= sb->map_nr)
 			index = 0;
-			alloc_hint = 0;
-		}

We need to set alloc_hint = 0 here for the round_robin case.

Good point, does need a reset for the loop for that case.

-- 
Jens Axboe