Re: [PATCH 3/4] blk-mq: use hw tag for scheduling if hw tag space is big enough

Jens Axboe
2017-04-28T18:22:45Z

On 04/28/2017 09:15 AM, Ming Lei wrote:
> +/*
> + * If this queue has enough hardware tags and doesn't share tags with
> + * other queues, just use hw tag directly for scheduling.
> + */
> +static inline bool blk_mq_sched_may_use_hw_tag(struct request_queue *q)
> +{
> + if (q->tag_set->flags & BLK_MQ_F_TAG_SHARED)
> + return false;
> +
> + if (blk_mq_get_queue_depth(q) < q->nr_requests)
> + return false;

I think we should leave a bigger gap. Ideally, for scheduling, we should
have a hw queue depth that's around half of what the scheduler has to
work with. That will always leave us something to schedule with, if the
hw can't deplete the whole pool.

--
Jens Axboe