Re: [PATCH v1 09/10] svcrdma: Use new CQ API for RPC-over-RDMA server receive CQs

[Devesh Sharma <devesh.sharma@broadcom.com>]

Looks good

On Wed, Feb 3, 2016 at 9:22 PM, Chuck Lever <chuck.lever@oracle.com> wrote:
> 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.
>
> 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 metrics are no longer updated.
>
> As far as I can tell, ib_alloc_cq() does not enable a consumer to
> specify a callback for handling async CQ events. This may cause
> a problem with handling spurious connection loss, though I think
> Receive completion flushing should be enough to force the server
> to clean up properly anyway.
>
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> ---
>  include/linux/sunrpc/svc_rdma.h          |    2
>  net/sunrpc/xprtrdma/svc_rdma_transport.c |  130 +++++++++---------------------
>  2 files changed, 41 insertions(+), 91 deletions(-)
>
> diff --git a/include/linux/sunrpc/svc_rdma.h b/include/linux/sunrpc/svc_rdma.h
> index 4ce7b74..7de9cbb 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 e7bda1e..316df77 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 +420,49 @@ 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_receive_wc - 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_receive_wc(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 at this point.     */
> +       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: Recv completion: %s (%u, vendor %u)\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 +635,7 @@ 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_receive_wc;
>         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 +660,7 @@ 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);
> @@ -1124,12 +1079,8 @@ 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;
> @@ -1225,7 +1176,6 @@ 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);
> @@ -1369,7 +1319,7 @@ 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);
>
> --
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