From 71b43531ee0be6dcaa406132ebd540022dcb12ea Mon Sep 17 00:00:00 2001 From: Chuck Lever Date: Sun, 4 Feb 2024 18:17:22 -0500 Subject: [PATCH] svcrdma: Post Send WR chain Eventually I'd like the server to post the reply's Send WR along with any Write WRs using only a single call to ib_post_send(), in order to reduce the NIC's doorbell rate. To do this, add an anchor for a WR chain to svc_rdma_send_ctxt, and refactor svc_rdma_send() to post this WR chain to the Send Queue. For the moment, the posted chain will continue to contain a single Send WR. Signed-off-by: Chuck Lever --- include/linux/sunrpc/svc_rdma.h | 6 ++- net/sunrpc/xprtrdma/svc_rdma_backchannel.c | 2 +- net/sunrpc/xprtrdma/svc_rdma_sendto.c | 49 +++++++++++++++------- 3 files changed, 38 insertions(+), 19 deletions(-) diff --git a/include/linux/sunrpc/svc_rdma.h b/include/linux/sunrpc/svc_rdma.h index e7595ae62fe2..ee05087d6499 100644 --- a/include/linux/sunrpc/svc_rdma.h +++ b/include/linux/sunrpc/svc_rdma.h @@ -210,6 +210,8 @@ struct svc_rdma_send_ctxt { struct svcxprt_rdma *sc_rdma; struct ib_send_wr sc_send_wr; + struct ib_send_wr *sc_wr_chain; + int sc_sqecount; struct ib_cqe sc_cqe; struct xdr_buf sc_hdrbuf; struct xdr_stream sc_stream; @@ -258,8 +260,8 @@ extern struct svc_rdma_send_ctxt * svc_rdma_send_ctxt_get(struct svcxprt_rdma *rdma); extern void svc_rdma_send_ctxt_put(struct svcxprt_rdma *rdma, struct svc_rdma_send_ctxt *ctxt); -extern int svc_rdma_send(struct svcxprt_rdma *rdma, - struct svc_rdma_send_ctxt *ctxt); +extern int svc_rdma_post_send(struct svcxprt_rdma *rdma, + struct svc_rdma_send_ctxt *ctxt); extern int svc_rdma_map_reply_msg(struct svcxprt_rdma *rdma, struct svc_rdma_send_ctxt *sctxt, const struct svc_rdma_pcl *write_pcl, diff --git a/net/sunrpc/xprtrdma/svc_rdma_backchannel.c b/net/sunrpc/xprtrdma/svc_rdma_backchannel.c index c9be6778643b..e5a78b761012 100644 --- a/net/sunrpc/xprtrdma/svc_rdma_backchannel.c +++ b/net/sunrpc/xprtrdma/svc_rdma_backchannel.c @@ -90,7 +90,7 @@ static int svc_rdma_bc_sendto(struct svcxprt_rdma *rdma, */ get_page(virt_to_page(rqst->rq_buffer)); sctxt->sc_send_wr.opcode = IB_WR_SEND; - return svc_rdma_send(rdma, sctxt); + return svc_rdma_post_send(rdma, sctxt); } /* Server-side transport endpoint wants a whole page for its send diff --git a/net/sunrpc/xprtrdma/svc_rdma_sendto.c b/net/sunrpc/xprtrdma/svc_rdma_sendto.c index 0ee9185f5f3f..0f02fb09d5b0 100644 --- a/net/sunrpc/xprtrdma/svc_rdma_sendto.c +++ b/net/sunrpc/xprtrdma/svc_rdma_sendto.c @@ -208,6 +208,9 @@ out: ctxt->sc_send_wr.num_sge = 0; ctxt->sc_cur_sge_no = 0; ctxt->sc_page_count = 0; + ctxt->sc_wr_chain = &ctxt->sc_send_wr; + ctxt->sc_sqecount = 1; + return ctxt; out_empty: @@ -293,7 +296,7 @@ static void svc_rdma_wc_send(struct ib_cq *cq, struct ib_wc *wc) struct svc_rdma_send_ctxt *ctxt = container_of(cqe, struct svc_rdma_send_ctxt, sc_cqe); - svc_rdma_wake_send_waiters(rdma, 1); + svc_rdma_wake_send_waiters(rdma, ctxt->sc_sqecount); if (unlikely(wc->status != IB_WC_SUCCESS)) goto flushed; @@ -312,36 +315,44 @@ flushed: } /** - * svc_rdma_send - Post a single Send WR - * @rdma: transport on which to post the WR - * @ctxt: send ctxt with a Send WR ready to post + * svc_rdma_post_send - Post a WR chain to the Send Queue + * @rdma: transport context + * @ctxt: WR chain to post * * Copy fields in @ctxt to stack variables in order to guarantee * that these values remain available after the ib_post_send() call. * In some error flow cases, svc_rdma_wc_send() releases @ctxt. * + * Note there is potential for starvation when the Send Queue is + * full because there is no order to when waiting threads are + * awoken. The transport is typically provisioned with a deep + * enough Send Queue that SQ exhaustion should be a rare event. + * * Return values: * %0: @ctxt's WR chain was posted successfully * %-ENOTCONN: The connection was lost */ -int svc_rdma_send(struct svcxprt_rdma *rdma, struct svc_rdma_send_ctxt *ctxt) +int svc_rdma_post_send(struct svcxprt_rdma *rdma, + struct svc_rdma_send_ctxt *ctxt) { - struct ib_send_wr *wr = &ctxt->sc_send_wr; + struct ib_send_wr *first_wr = ctxt->sc_wr_chain; + struct ib_send_wr *send_wr = &ctxt->sc_send_wr; + const struct ib_send_wr *bad_wr = first_wr; struct rpc_rdma_cid cid = ctxt->sc_cid; - int ret; + int ret, sqecount = ctxt->sc_sqecount; might_sleep(); /* Sync the transport header buffer */ ib_dma_sync_single_for_device(rdma->sc_pd->device, - wr->sg_list[0].addr, - wr->sg_list[0].length, + send_wr->sg_list[0].addr, + send_wr->sg_list[0].length, DMA_TO_DEVICE); /* If the SQ is full, wait until an SQ entry is available */ while (!test_bit(XPT_CLOSE, &rdma->sc_xprt.xpt_flags)) { - if ((atomic_dec_return(&rdma->sc_sq_avail) < 0)) { - svc_rdma_wake_send_waiters(rdma, 1); + if (atomic_sub_return(sqecount, &rdma->sc_sq_avail) < 0) { + svc_rdma_wake_send_waiters(rdma, sqecount); /* When the transport is torn down, assume * ib_drain_sq() will trigger enough Send @@ -358,12 +369,18 @@ int svc_rdma_send(struct svcxprt_rdma *rdma, struct svc_rdma_send_ctxt *ctxt) } trace_svcrdma_post_send(ctxt); - ret = ib_post_send(rdma->sc_qp, wr, NULL); + ret = ib_post_send(rdma->sc_qp, first_wr, &bad_wr); if (ret) { trace_svcrdma_sq_post_err(rdma, &cid, ret); svc_xprt_deferred_close(&rdma->sc_xprt); - svc_rdma_wake_send_waiters(rdma, 1); - break; + + /* If even one WR was posted, there will be a + * Send completion that bumps sc_sq_avail. + */ + if (bad_wr == first_wr) { + svc_rdma_wake_send_waiters(rdma, sqecount); + break; + } } return 0; } @@ -884,7 +901,7 @@ static int svc_rdma_send_reply_msg(struct svcxprt_rdma *rdma, sctxt->sc_send_wr.opcode = IB_WR_SEND; } - return svc_rdma_send(rdma, sctxt); + return svc_rdma_post_send(rdma, sctxt); } /** @@ -948,7 +965,7 @@ void svc_rdma_send_error_msg(struct svcxprt_rdma *rdma, sctxt->sc_send_wr.num_sge = 1; sctxt->sc_send_wr.opcode = IB_WR_SEND; sctxt->sc_sges[0].length = sctxt->sc_hdrbuf.len; - if (svc_rdma_send(rdma, sctxt)) + if (svc_rdma_post_send(rdma, sctxt)) goto put_ctxt; return;