On Wed, May 07, 2025 at 03:49:36PM -0600, Uday Shankar wrote:
In update_alloc_hint_after_get, we wrap the new hint back to 0 one bit too early. This breaks round robin tag allocation (BLK_MQ_F_TAG_RR) - some tags get skipped, so we don't get round robin tags even in the simple case of single-threaded load on a single hctx. Fix the off-by-one in the wrapping condition so that round robin tag allocation works properly.
The same pattern occurs in __sbitmap_get_word, so fix it there too.
Signed-off-by: Uday Shankar ushankar@purestorage.com
lib/sbitmap.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/lib/sbitmap.c b/lib/sbitmap.c index d3412984170c03dc6600bbe53f130404b765ac5a..aa1cec78b9649f1f3e8ef2d617dd7ee724391a8c 100644 --- a/lib/sbitmap.c +++ b/lib/sbitmap.c @@ -51,7 +51,7 @@ static inline void update_alloc_hint_after_get(struct sbitmap *sb, } else if (nr == hint || unlikely(sb->round_robin)) { /* Only update the hint if we used it. */ hint = nr + 1;
if (hint >= depth - 1)
if (hint >= depth) hint = 0;
This may help for round robin.
} @@ -182,7 +182,7 @@ static int __sbitmap_get_word(unsigned long *word, unsigned long depth, break; hint = nr + 1;
if (hint >= depth - 1)
if (hint >= depth) hint = 0;
I guess round robin may need to return -1 if 'hint >= depth'.
Also the existing behavior starts from adding sbitmap, maybe Jens has idea why hint is checked against 'depth -1' instead of 'depth'.
Thanks, Ming