On Tue, 2017-12-12 at 11:01 -0800, Tejun Heo wrote:
> +/*
> + * Bits for request->gstate. The lower two bits carry MQ_RQ_* state value
> + * and the upper bits the generation number.
> + */
> +enum mq_rq_state {
> + MQ_RQ_IDLE = 0,
> + MQ_RQ_IN_FLIGHT = 1,
> +
> + MQ_RQ_STATE_BITS = 2,
> + MQ_RQ_STATE_MASK = (1 << MQ_RQ_STATE_BITS) - 1,
> + MQ_RQ_GEN_INC = 1 << MQ_RQ_STATE_BITS,
> +};
> +
> @@ -85,6 +98,38 @@ extern void blk_mq_rq_timed_out(struct request *req, bool
> reserved);
> +/**
> + * blk_mq_rq_state() - read the current MQ_RQ_* state of a request
> + * @rq: target request.
> + */
> +static inline int blk_mq_rq_state(struct request *rq)
> +{
> + return READ_ONCE(rq->gstate) & MQ_RQ_STATE_MASK;
> +}
> +
> +/**
> + * blk_mq_rq_update_state() - set the current MQ_RQ_* state of a request
> + * @rq: target request.
> + * @state: new state to set.
> + *
> + * Set @rq's state to @state. The caller is responsible for ensuring that
> + * there are no other updaters. A request can transition into IN_FLIGHT
> + * only from IDLE and doing so increments the generation number.
> + */
> +static inline void blk_mq_rq_update_state(struct request *rq,
> + enum mq_rq_state state)
> +{
> + u64 new_val = (READ_ONCE(rq->gstate) & ~MQ_RQ_STATE_MASK) | state;
> +
> + if (state == MQ_RQ_IN_FLIGHT) {
> + WARN_ON_ONCE(blk_mq_rq_state(rq) != MQ_RQ_IDLE);
> + new_val += MQ_RQ_GEN_INC;
> + }
> +
> + /* avoid exposing interim values */
> + WRITE_ONCE(rq->gstate, new_val);
> +}
Hello Tejun,
Have you considered the following instead of introducing MQ_RQ_IDLE and
MQ_RQ_IN_FLIGHT? I think this could help to limit the number of new atomic
operations introduced in the hot path by this patch series.
static inline bool blk_mq_rq_in_flight(struct request *rq)
{
return list_empty(&rq->queuelist);
}
Thanks,
Bart.
