On Tue, Jan 11, 2022 at 10:02:16PM +0800, Laibin Qiu wrote:
> In case of shared tags, there might be more than one hctx which
> allocates from the same tags, and each hctx is limited to allocate at
> most:
> hctx_max_depth = max((bt->sb.depth + users - 1) / users, 4U);
>
> tag idle detection is lazy, and may be delayed for 30sec, so there
> could be just one real active hctx(queue) but all others are actually
> idle and still accounted as active because of the lazy idle detection.
> Then if wake_batch is > hctx_max_depth, driver tag allocation may wait
> forever on this real active hctx.
>
> Fix this by recalculating wake_batch when inc or dec active_queues.
...
> {
> + unsigned int users;
Missed blank line here.
> if (blk_mq_is_shared_tags(hctx->flags)) {
> struct request_queue *q = hctx->queue;
>
> + if (test_bit(QUEUE_FLAG_HCTX_ACTIVE, &q->queue_flags) ||
> + test_and_set_bit(QUEUE_FLAG_HCTX_ACTIVE, &q->queue_flags)) {
Whoever wrote this code did too much defensive programming, because the first
conditional doesn't make much sense here. Am I right?
> + return true;
> + }
> } else {
> + if (test_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state) ||
> + test_and_set_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state)) {
Ditto.
> + return true;
> + }
> }
...
> + unsigned int wake_batch = clamp_t(unsigned int,
> + (sbq->sb.depth + users - 1) / users, 4U, SBQ_WAKE_BATCH);
unsigned int wake_batch;
wake_batch = clamp_val((sbq->sb.depth + users - 1) / users, 4, SBQ_WAKE_BATCH);
...
is easier to read, no?
--
With Best Regards,
Andy Shevchenko
