svcrdma: Use new CQ API for RPC-over-RDMA server receive CQs

Calling ib_poll_cq() to sort through WCs during a completion is a
common pattern amongst RDMA consumers. Since commit 14d3a3b2498e
("IB: add a proper completion queue abstraction"), WC sorting can
be handled by the IB core.

By converting to this new API, svcrdma is made a better neighbor to
other RDMA consumers, as it allows the core to schedule the delivery
of completions more fairly amongst all active consumers.

Because each ib_cqe carries a pointer to a completion method, the
core can now post operations on a consumer's QP, and handle the
completions itself.

svcrdma receive completions no longer use the dto_tasklet. Each
polled Receive WC is now handled individually in soft IRQ context.

The server transport's rdma_stat_rq_poll and rdma_stat_rq_prod
metrics are no longer updated.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

2 files changed, 40 insertions, 91 deletions

diff --git a/include/linux/sunrpc/svc_rdma.h b/include/linux/sunrpc/svc_rdma.h
index c2b0d95602d8..cf79ab86d3d4 100644
--- a/include/linux/sunrpc/svc_rdma.h
+++ b/include/linux/sunrpc/svc_rdma.h
@@ -75,6 +75,7 @@ struct svc_rdma_op_ctxt {
         struct svc_rdma_fastreg_mr *frmr;
         int hdr_count;
         struct xdr_buf arg;
+        struct ib_cqe cqe;
         struct list_head dto_q;
         enum ib_wr_opcode wr_op;
         enum ib_wc_status wc_status;
@@ -174,7 +175,6 @@ struct svcxprt_rdma {
         struct work_struct   sc_work;
 };
 /* sc_flags */
-#define RDMAXPRT_RQ_PENDING     1
 #define RDMAXPRT_SQ_PENDING     2
 #define RDMAXPRT_CONN_PENDING   3
 
diff --git a/net/sunrpc/xprtrdma/svc_rdma_transport.c b/net/sunrpc/xprtrdma/svc_rdma_transport.c
index 15c8fa3ee794..5dfa1b6bf0c2 100644
--- a/net/sunrpc/xprtrdma/svc_rdma_transport.c
+++ b/net/sunrpc/xprtrdma/svc_rdma_transport.c
@@ -68,7 +68,6 @@ static void svc_rdma_detach(struct svc_xprt *xprt);
 static void svc_rdma_free(struct svc_xprt *xprt);
 static int svc_rdma_has_wspace(struct svc_xprt *xprt);
 static int svc_rdma_secure_port(struct svc_rqst *);
-static void rq_cq_reap(struct svcxprt_rdma *xprt);
 static void sq_cq_reap(struct svcxprt_rdma *xprt);
 
 static DECLARE_TASKLET(dto_tasklet, dto_tasklet_func, 0UL);
@@ -413,7 +412,6 @@ static void dto_tasklet_func(unsigned long data)
                 list_del_init(&xprt->sc_dto_q);
                 spin_unlock_irqrestore(&dto_lock, flags);
 
-                rq_cq_reap(xprt);
                 sq_cq_reap(xprt);
 
                 svc_xprt_put(&xprt->sc_xprt);
@@ -422,93 +420,48 @@ static void dto_tasklet_func(unsigned long data)
         spin_unlock_irqrestore(&dto_lock, flags);
 }
 
-/*
- * Receive Queue Completion Handler
- *
- * Since an RQ completion handler is called on interrupt context, we
- * need to defer the handling of the I/O to a tasklet
- */
-static void rq_comp_handler(struct ib_cq *cq, void *cq_context)
-{
-        struct svcxprt_rdma *xprt = cq_context;
-        unsigned long flags;
-
-        /* Guard against unconditional flush call for destroyed QP */
-        if (atomic_read(&xprt->sc_xprt.xpt_ref.refcount)==0)
-                return;
-
-        /*
-         * Set the bit regardless of whether or not it's on the list
-         * because it may be on the list already due to an SQ
-         * completion.
-         */
-        set_bit(RDMAXPRT_RQ_PENDING, &xprt->sc_flags);
-
-        /*
-         * If this transport is not already on the DTO transport queue,
-         * add it
-         */
-        spin_lock_irqsave(&dto_lock, flags);
-        if (list_empty(&xprt->sc_dto_q)) {
-                svc_xprt_get(&xprt->sc_xprt);
-                list_add_tail(&xprt->sc_dto_q, &dto_xprt_q);
-        }
-        spin_unlock_irqrestore(&dto_lock, flags);
-
-        /* Tasklet does all the work to avoid irqsave locks. */
-        tasklet_schedule(&dto_tasklet);
-}
-
-/*
- * rq_cq_reap - Process the RQ CQ.
+/**
+ * svc_rdma_wc_receive - Invoked by RDMA provider for each polled Receive WC
+ * @cq:        completion queue
+ * @wc:        completed WR
  *
- * Take all completing WC off the CQE and enqueue the associated DTO
- * context on the dto_q for the transport.
- *
- * Note that caller must hold a transport reference.
  */
-static void rq_cq_reap(struct svcxprt_rdma *xprt)
+static void svc_rdma_wc_receive(struct ib_cq *cq, struct ib_wc *wc)
 {
-        int ret;
-        struct ib_wc wc;
-        struct svc_rdma_op_ctxt *ctxt = NULL;
-
-        if (!test_and_clear_bit(RDMAXPRT_RQ_PENDING, &xprt->sc_flags))
-                return;
+        struct svcxprt_rdma *xprt = cq->cq_context;
+        struct ib_cqe *cqe = wc->wr_cqe;
+        struct svc_rdma_op_ctxt *ctxt;
 
-        ib_req_notify_cq(xprt->sc_rq_cq, IB_CQ_NEXT_COMP);
-        atomic_inc(&rdma_stat_rq_poll);
+        /* WARNING: Only wc->wr_cqe and wc->status are reliable */
+        ctxt = container_of(cqe, struct svc_rdma_op_ctxt, cqe);
+        ctxt->wc_status = wc->status;
+        svc_rdma_unmap_dma(ctxt);
 
-        while ((ret = ib_poll_cq(xprt->sc_rq_cq, 1, &wc)) > 0) {
-                ctxt = (struct svc_rdma_op_ctxt *)(unsigned long)wc.wr_id;
-                ctxt->wc_status = wc.status;
-                ctxt->byte_len = wc.byte_len;
-                svc_rdma_unmap_dma(ctxt);
-                if (wc.status != IB_WC_SUCCESS) {
-                        /* Close the transport */
-                        dprintk("svcrdma: transport closing putting ctxt %p\n", ctxt);
-                        set_bit(XPT_CLOSE, &xprt->sc_xprt.xpt_flags);
-                        svc_rdma_put_context(ctxt, 1);
-                        svc_xprt_put(&xprt->sc_xprt);
-                        continue;
-                }
-                spin_lock_bh(&xprt->sc_rq_dto_lock);
-                list_add_tail(&ctxt->dto_q, &xprt->sc_rq_dto_q);
-                spin_unlock_bh(&xprt->sc_rq_dto_lock);
-                svc_xprt_put(&xprt->sc_xprt);
-        }
+        if (wc->status != IB_WC_SUCCESS)
+                goto flushed;
 
-        if (ctxt)
-                atomic_inc(&rdma_stat_rq_prod);
+        /* All wc fields are now known to be valid */
+        ctxt->byte_len = wc->byte_len;
+        spin_lock(&xprt->sc_rq_dto_lock);
+        list_add_tail(&ctxt->dto_q, &xprt->sc_rq_dto_q);
+        spin_unlock(&xprt->sc_rq_dto_lock);
 
         set_bit(XPT_DATA, &xprt->sc_xprt.xpt_flags);
-        /*
-         * If data arrived before established event,
-         * don't enqueue. This defers RPC I/O until the
-         * RDMA connection is complete.
-         */
-        if (!test_bit(RDMAXPRT_CONN_PENDING, &xprt->sc_flags))
-                svc_xprt_enqueue(&xprt->sc_xprt);
+        if (test_bit(RDMAXPRT_CONN_PENDING, &xprt->sc_flags))
+                goto out;
+        svc_xprt_enqueue(&xprt->sc_xprt);
+        goto out;
+
+flushed:
+        if (wc->status != IB_WC_WR_FLUSH_ERR)
+                pr_warn("svcrdma: receive: %s (%u/0x%x)\n",
+                        ib_wc_status_msg(wc->status),
+                        wc->status, wc->vendor_err);
+        set_bit(XPT_CLOSE, &xprt->sc_xprt.xpt_flags);
+        svc_rdma_put_context(ctxt, 1);
+
+out:
+        svc_xprt_put(&xprt->sc_xprt);
 }
 
 /*
@@ -681,6 +634,7 @@ int svc_rdma_post_recv(struct svcxprt_rdma *xprt, gfp_t flags)
         ctxt = svc_rdma_get_context(xprt);
         buflen = 0;
         ctxt->direction = DMA_FROM_DEVICE;
+        ctxt->cqe.done = svc_rdma_wc_receive;
         for (sge_no = 0; buflen < xprt->sc_max_req_size; sge_no++) {
                 if (sge_no >= xprt->sc_max_sge) {
                         pr_err("svcrdma: Too many sges (%d)\n", sge_no);
@@ -705,7 +659,7 @@ int svc_rdma_post_recv(struct svcxprt_rdma *xprt, gfp_t flags)
         recv_wr.next = NULL;
         recv_wr.sg_list = &ctxt->sge[0];
         recv_wr.num_sge = ctxt->count;
-        recv_wr.wr_id = (u64)(unsigned long)ctxt;
+        recv_wr.wr_cqe = &ctxt->cqe;
 
         svc_xprt_get(&xprt->sc_xprt);
         ret = ib_post_recv(xprt->sc_qp, &recv_wr, &bad_recv_wr);
@@ -1094,12 +1048,8 @@ static struct svc_xprt *svc_rdma_accept(struct svc_xprt *xprt)
                 dprintk("svcrdma: error creating SQ CQ for connect request\n");
                 goto errout;
         }
-        cq_attr.cqe = newxprt->sc_rq_depth;
-        newxprt->sc_rq_cq = ib_create_cq(dev,
-                                         rq_comp_handler,
-                                         cq_event_handler,
-                                         newxprt,
-                                         &cq_attr);
+        newxprt->sc_rq_cq = ib_alloc_cq(dev, newxprt, newxprt->sc_rq_depth,
+                                        0, IB_POLL_SOFTIRQ);
         if (IS_ERR(newxprt->sc_rq_cq)) {
                 dprintk("svcrdma: error creating RQ CQ for connect request\n");
                 goto errout;
@@ -1193,7 +1143,6 @@ static struct svc_xprt *svc_rdma_accept(struct svc_xprt *xprt)
          * miss the first message
          */
         ib_req_notify_cq(newxprt->sc_sq_cq, IB_CQ_NEXT_COMP);
-        ib_req_notify_cq(newxprt->sc_rq_cq, IB_CQ_NEXT_COMP);
 
         /* Accept Connection */
         set_bit(RDMAXPRT_CONN_PENDING, &newxprt->sc_flags);
@@ -1337,7 +1286,7 @@ static void __svc_rdma_free(struct work_struct *work)
                 ib_destroy_cq(rdma->sc_sq_cq);
 
         if (rdma->sc_rq_cq && !IS_ERR(rdma->sc_rq_cq))
-                ib_destroy_cq(rdma->sc_rq_cq);
+                ib_free_cq(rdma->sc_rq_cq);
 
         if (rdma->sc_pd && !IS_ERR(rdma->sc_pd))
                 ib_dealloc_pd(rdma->sc_pd);