[PATCH v1 1/3] svcrdma: Fewer calls to wake_up() in Send completion handler
From: Chuck Lever <chuck.lever@oracle.com>
Date: 2021-07-26 14:47:00
Also in:
linux-nfs
Subsystem:
kernel nfsd, sunrpc, and lockd servers, networking [general], nfs, sunrpc, and lockd clients, the rest · Maintainers:
Chuck Lever, Jeff Layton, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Trond Myklebust, Anna Schumaker, Linus Torvalds
Because wake_up() takes an IRQ-safe lock, it can be expensive, especially to call inside of a single-threaded completion handler. What's more, the Send wait queue almost never has waiters, so most of the time, this is an expensive no-op. As always, the goal is to reduce the average overhead of each completion, because a transport's completion handlers are single- threaded on one CPU core. This change reduces CPU utilization of the Send completion thread by 2-3% on my server. Signed-off-by: Chuck Lever <chuck.lever@oracle.com> --- include/linux/sunrpc/svc_rdma.h | 1 + net/sunrpc/xprtrdma/svc_rdma_rw.c | 7 ++----- net/sunrpc/xprtrdma/svc_rdma_sendto.c | 18 +++++++++++++++--- 3 files changed, 18 insertions(+), 8 deletions(-)
diff --git a/include/linux/sunrpc/svc_rdma.h b/include/linux/sunrpc/svc_rdma.h
index 3184465de3a0..57c60ffe76dd 100644
--- a/include/linux/sunrpc/svc_rdma.h
+++ b/include/linux/sunrpc/svc_rdma.h@@ -207,6 +207,7 @@ extern void svc_rdma_send_error_msg(struct svcxprt_rdma *rdma, struct svc_rdma_send_ctxt *sctxt, struct svc_rdma_recv_ctxt *rctxt, int status); +extern void svc_rdma_wake_send_waiters(struct svcxprt_rdma *rdma, int avail); extern int svc_rdma_sendto(struct svc_rqst *); extern int svc_rdma_result_payload(struct svc_rqst *rqstp, unsigned int offset, unsigned int length);
diff --git a/net/sunrpc/xprtrdma/svc_rdma_rw.c b/net/sunrpc/xprtrdma/svc_rdma_rw.c
index 1e651447dc4e..3d1b119f6e3e 100644
--- a/net/sunrpc/xprtrdma/svc_rdma_rw.c
+++ b/net/sunrpc/xprtrdma/svc_rdma_rw.c@@ -248,8 +248,7 @@ static void svc_rdma_write_done(struct ib_cq *cq, struct ib_wc *wc) trace_svcrdma_wc_write(wc, &cc->cc_cid); - atomic_add(cc->cc_sqecount, &rdma->sc_sq_avail); - wake_up(&rdma->sc_send_wait); + svc_rdma_wake_send_waiters(rdma, cc->cc_sqecount); if (unlikely(wc->status != IB_WC_SUCCESS)) svc_xprt_deferred_close(&rdma->sc_xprt);
@@ -304,9 +303,7 @@ static void svc_rdma_wc_read_done(struct ib_cq *cq, struct ib_wc *wc) trace_svcrdma_wc_read(wc, &cc->cc_cid); - atomic_add(cc->cc_sqecount, &rdma->sc_sq_avail); - wake_up(&rdma->sc_send_wait); - + svc_rdma_wake_send_waiters(rdma, cc->cc_sqecount); cc->cc_status = wc->status; complete(&cc->cc_done); return;
diff --git a/net/sunrpc/xprtrdma/svc_rdma_sendto.c b/net/sunrpc/xprtrdma/svc_rdma_sendto.c
index d6bbafb773e1..fba2ee4eb607 100644
--- a/net/sunrpc/xprtrdma/svc_rdma_sendto.c
+++ b/net/sunrpc/xprtrdma/svc_rdma_sendto.c@@ -258,6 +258,20 @@ void svc_rdma_send_ctxt_put(struct svcxprt_rdma *rdma, spin_unlock(&rdma->sc_send_lock); } +/** + * svc_rdma_wake_send_waiters - manage Send Queue accounting + * @rdma: controlling transport + * @avail: Number of additional SQEs that are now available + * + */ +void svc_rdma_wake_send_waiters(struct svcxprt_rdma *rdma, int avail) +{ + atomic_add(avail, &rdma->sc_sq_avail); + smp_mb__after_atomic(); + if (unlikely(waitqueue_active(&rdma->sc_send_wait))) + wake_up(&rdma->sc_send_wait); +} + /** * svc_rdma_wc_send - Invoked by RDMA provider for each polled Send WC * @cq: Completion Queue context
@@ -275,11 +289,9 @@ static void svc_rdma_wc_send(struct ib_cq *cq, struct ib_wc *wc) trace_svcrdma_wc_send(wc, &ctxt->sc_cid); + svc_rdma_wake_send_waiters(rdma, 1); complete(&ctxt->sc_done); - atomic_inc(&rdma->sc_sq_avail); - wake_up(&rdma->sc_send_wait); - if (unlikely(wc->status != IB_WC_SUCCESS)) svc_xprt_deferred_close(&rdma->sc_xprt); }