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authorChuck Lever <chuck.lever@oracle.com>2024-02-04 18:17:22 -0500
committerChuck Lever <chuck.lever@oracle.com>2024-03-01 09:12:28 -0500
commit71b43531ee0be6dcaa406132ebd540022dcb12ea (patch)
tree5530d7ca8247eb9c69474dc1799e454cb0746c59 /net/sunrpc
parentfc709d82dda6405862a681cc425386bfaf049539 (diff)
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 <chuck.lever@oracle.com>
Diffstat (limited to 'net/sunrpc')
-rw-r--r--net/sunrpc/xprtrdma/svc_rdma_backchannel.c2
-rw-r--r--net/sunrpc/xprtrdma/svc_rdma_sendto.c49
2 files changed, 34 insertions, 17 deletions
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;