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: 9cb837480424e ("RDMA/rtrs: server: main functionality")
Link: https://lore.kernel.org/r/20210528113018.52290-14-jinpu.wang@ionos.com
Signed-off-by: Md Haris Iqbal <haris.iqbal@ionos.com>
Signed-off-by: Jack Wang <jinpu.wang@ionos.com>
Signed-off-by: Gioh Kim <gi-oh.kim@ionos.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

diff --git a/drivers/infiniband/ulp/rtrs/rtrs-srv-stats.c b/drivers/infiniband/ulp/rtrs/rtrs-srv-stats.c
index e102b13..520c247 100644 (file)
--- a/drivers/infiniband/ulp/rtrs/rtrs-srv-stats.c
+++ b/drivers/infiniband/ulp/rtrs/rtrs-srv-stats.c
@@ -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",
-                        (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));
+       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), 0);
 }

diff --git a/drivers/infiniband/ulp/rtrs/rtrs-srv.c b/drivers/infiniband/ulp/rtrs/rtrs-srv.c
index 840a342..631d379 100644 (file)
--- a/drivers/infiniband/ulp/rtrs/rtrs-srv.c
+++ b/drivers/infiniband/ulp/rtrs/rtrs-srv.c
@@ -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 @@ err:
 
 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);

diff --git a/drivers/infiniband/ulp/rtrs/rtrs-srv.h b/drivers/infiniband/ulp/rtrs/rtrs-srv.h
index 9543ae1..f8da2e3 100644 (file)
--- a/drivers/infiniband/ulp/rtrs/rtrs-srv.h
+++ b/drivers/infiniband/ulp/rtrs/rtrs-srv.h
@@ -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;