Commit 704f3f64 authored by Chuck Lever's avatar Chuck Lever Committed by Trond Myklebust
Browse files

xprtrdma: Post receive buffers after RPC completion 



rpcrdma_post_recvs() runs in CQ poll context and its cost
falls on the latency-critical path between polling a Receive
completion and waking the RPC consumer. Every cycle spent
refilling the Receive Queue delays delivery of the reply to
the NFS layer.

Move the rpcrdma_post_recvs() call in rpcrdma_reply_handler()
to after the RPC has been decoded and completed. The larger
batch size from the preceding patch provides sufficient
Receive Queue headroom to absorb the brief delay before
buffers are replenished.

Signed-off-by: default avatarChuck Lever <chuck.lever@oracle.com>
Signed-off-by: default avatarTrond Myklebust <trond.myklebust@hammerspace.com>
parent 93b4791a

net/sunrpc/xprtrdma/rpc_rdma.c

+9 −5
Original line number Diff line number Diff line
@@ -1422,7 +1422,6 @@ void rpcrdma_reply_handler(struct rpcrdma_rep *rep) 
		credits = 1;	/* don't deadlock */

	else if (credits > r_xprt->rx_ep->re_max_requests)

		credits = r_xprt->rx_ep->re_max_requests;

	rpcrdma_post_recvs(r_xprt, credits + (buf->rb_bc_srv_max_requests << 1));

	if (buf->rb_credits != credits)

		rpcrdma_update_cwnd(r_xprt, credits);
@@ -1441,15 +1440,20 @@ void rpcrdma_reply_handler(struct rpcrdma_rep *rep) 
		/* LocalInv completion will complete the RPC */

	else

		kref_put(&req->rl_kref, rpcrdma_reply_done);

	return;



out_badversion:

	trace_xprtrdma_reply_vers_err(rep);

	goto out;

out_post:

	rpcrdma_post_recvs(r_xprt,

			   credits + (buf->rb_bc_srv_max_requests << 1));

	return;



out_norqst:

	spin_unlock(&xprt->queue_lock);

	trace_xprtrdma_reply_rqst_err(rep);

	rpcrdma_rep_put(buf, rep);

	goto out_post;



out_badversion:

	trace_xprtrdma_reply_vers_err(rep);

	goto out;



out_shortreply: