Commit 0cdfb3b2 authored by Md Haris Iqbal's avatar Md Haris Iqbal Committed by Jason Gunthorpe
Browse files

RDMA/rtrs-srv: Replace atomic_t with percpu_ref for ids_inflight 

ids_inflight is used to track the inflight IOs. But the use of atomic_t
variable can cause performance drops and can also become a performance
bottleneck.

This commit replaces the use of atomic_t with a percpu_ref structure. The
advantage it offers is, it doesn't check if the reference has fallen to 0,
until the user explicitly signals it to; and that is done by the
percpu_ref_kill() function call. After that, the percpu_ref structure
behaves like an atomic_t and for every put call, checks whether the
reference has fallen to 0 or not.

rtrs_srv_stats_rdma_to_str shows the count of ids_inflight as 0
for user-mode tools not to be confused.

Fixes: 9cb83748 ("RDMA/rtrs: server: main functionality")
Link: https://lore.kernel.org/r/20210528113018.52290-14-jinpu.wang@ionos.com


Signed-off-by: default avatarMd Haris Iqbal <haris.iqbal@ionos.com>
Signed-off-by: default avatarJack Wang <jinpu.wang@ionos.com>
Signed-off-by: default avatarGioh Kim <gi-oh.kim@ionos.com>
Signed-off-by: default avatarJason Gunthorpe <jgg@nvidia.com>
parent 41db63a7

drivers/infiniband/ulp/rtrs/rtrs-srv-stats.c

+5 −7
Original line number Diff line number Diff line
@@ -27,12 +27,10 @@ ssize_t rtrs_srv_stats_rdma_to_str(struct rtrs_srv_stats *stats, 
				    char *page, size_t len)

{

	struct rtrs_srv_stats_rdma_stats *r = &stats->rdma_stats;

	struct rtrs_srv_sess *sess = stats->sess;



	return scnprintf(page, len, "%lld %lld %lld %lld %u\n",

	return scnprintf(page, len, "%lld %lld %lld %lldn %u\n",

			  (s64)atomic64_read(&r->dir[READ].cnt),

			  (s64)atomic64_read(&r->dir[READ].size_total),

			  (s64)atomic64_read(&r->dir[WRITE].cnt),

			 (s64)atomic64_read(&r->dir[WRITE].size_total),

			 atomic_read(&sess->ids_inflight));

			  (s64)atomic64_read(&r->dir[WRITE].size_total), 0);

}

drivers/infiniband/ulp/rtrs/rtrs-srv.c

+28 −15
Original line number Diff line number Diff line
@@ -111,7 +111,6 @@ static void rtrs_srv_free_ops_ids(struct rtrs_srv_sess *sess) 
	struct rtrs_srv *srv = sess->srv;

	int i;



	WARN_ON(atomic_read(&sess->ids_inflight));

	if (sess->ops_ids) {

		for (i = 0; i < srv->queue_depth; i++)

			free_id(sess->ops_ids[i]);
@@ -126,11 +125,19 @@ static struct ib_cqe io_comp_cqe = { 
	.done = rtrs_srv_rdma_done

};



static inline void rtrs_srv_inflight_ref_release(struct percpu_ref *ref)

{

	struct rtrs_srv_sess *sess = container_of(ref, struct rtrs_srv_sess, ids_inflight_ref);



	percpu_ref_exit(&sess->ids_inflight_ref);

	complete(&sess->complete_done);

}



static int rtrs_srv_alloc_ops_ids(struct rtrs_srv_sess *sess)

{

	struct rtrs_srv *srv = sess->srv;

	struct rtrs_srv_op *id;

	int i;

	int i, ret;



	sess->ops_ids = kcalloc(srv->queue_depth, sizeof(*sess->ops_ids),

				GFP_KERNEL);
@@ -144,8 +151,14 @@ static int rtrs_srv_alloc_ops_ids(struct rtrs_srv_sess *sess) 


		sess->ops_ids[i] = id;

	}

	init_waitqueue_head(&sess->ids_waitq);

	atomic_set(&sess->ids_inflight, 0);



	ret = percpu_ref_init(&sess->ids_inflight_ref,

			      rtrs_srv_inflight_ref_release, 0, GFP_KERNEL);

	if (ret) {

		pr_err("Percpu reference init failed\n");

		goto err;

	}

	init_completion(&sess->complete_done);



	return 0;
@@ -156,21 +169,14 @@ static int rtrs_srv_alloc_ops_ids(struct rtrs_srv_sess *sess) 


static inline void rtrs_srv_get_ops_ids(struct rtrs_srv_sess *sess)

{

	atomic_inc(&sess->ids_inflight);

	percpu_ref_get(&sess->ids_inflight_ref);

}



static inline void rtrs_srv_put_ops_ids(struct rtrs_srv_sess *sess)

{

	if (atomic_dec_and_test(&sess->ids_inflight))

		wake_up(&sess->ids_waitq);

	percpu_ref_put(&sess->ids_inflight_ref);

}



static void rtrs_srv_wait_ops_ids(struct rtrs_srv_sess *sess)

{

	wait_event(sess->ids_waitq, !atomic_read(&sess->ids_inflight));

}





static void rtrs_srv_reg_mr_done(struct ib_cq *cq, struct ib_wc *wc)

{

	struct rtrs_srv_con *con = to_srv_con(wc->qp->qp_context);
@@ -1479,8 +1485,15 @@ static void rtrs_srv_close_work(struct work_struct *work) 
		rdma_disconnect(con->c.cm_id);

		ib_drain_qp(con->c.qp);

	}

	/* Wait for all inflights */

	rtrs_srv_wait_ops_ids(sess);



	/*

	 * Degrade ref count to the usual model with a single shared

	 * atomic_t counter

	 */

	percpu_ref_kill(&sess->ids_inflight_ref);



	/* Wait for all completion */

	wait_for_completion(&sess->complete_done);



	/* Notify upper layer if we are the last path */

	rtrs_srv_sess_down(sess);

drivers/infiniband/ulp/rtrs/rtrs-srv.h

+2 −2
Original line number Diff line number Diff line
@@ -81,8 +81,8 @@ struct rtrs_srv_sess { 
	spinlock_t		state_lock;

	int			cur_cq_vector;

	struct rtrs_srv_op	**ops_ids;

	atomic_t		ids_inflight;

	wait_queue_head_t	ids_waitq;

	struct percpu_ref       ids_inflight_ref;

	struct completion       complete_done;

	struct rtrs_srv_mr	*mrs;

	unsigned int		mrs_num;

	dma_addr_t		*dma_addr;