Commit 6c8c84f5 authored by Chuck Lever's avatar Chuck Lever
Browse files

svcrdma: Fewer calls to wake_up() in Send completion handler 



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: default avatarChuck Lever <chuck.lever@oracle.com>
Reviewed-By: default avatarTom Talpey <tom@talpey.com>
parent cd2d644d

include/linux/sunrpc/svc_rdma.h

+1 −0
Original line number Diff line number Diff line
@@ -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);

net/sunrpc/xprtrdma/svc_rdma_rw.c

+2 −5
Original line number Diff line number Diff line
@@ -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;

net/sunrpc/xprtrdma/svc_rdma_sendto.c

+15 −3
Original line number Diff line number Diff line
@@ -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);

}