Commit 93b4791a authored by Chuck Lever's avatar Chuck Lever Committed by Trond Myklebust
Browse files

xprtrdma: Scale receive batch size with credit window 



The fixed RPCRDMA_MAX_RECV_BATCH of 7 results in frequent
small ib_post_recv batches during high-rate workloads. With
a 128-slot credit window, receives are reposted every 7th
completion, each batch incurring atomic serialization and a
doorbell write.

Replace the fixed batch constant with a per-endpoint value
scaled to 25% of the negotiated credit window. For a typical
128-credit connection this raises the batch from 7 to 32,
reducing doorbell frequency by roughly 4x and amortizing the
per-batch atomic and MMIO costs over a larger group of
receive WRs.

Signed-off-by: default avatarChuck Lever <chuck.lever@oracle.com>
Signed-off-by: default avatarTrond Myklebust <trond.myklebust@hammerspace.com>
parent 7a079ab5

net/sunrpc/xprtrdma/frwr_ops.c

+2 −1
Original line number Diff line number Diff line
@@ -244,9 +244,10 @@ int frwr_query_device(struct rpcrdma_ep *ep, const struct ib_device *device) 
	}

	ep->re_attr.cap.max_send_wr += RPCRDMA_BACKWARD_WRS;

	ep->re_attr.cap.max_send_wr += 1; /* for ib_drain_sq */

	ep->re_recv_batch = ep->re_max_requests >> 2;

	ep->re_attr.cap.max_recv_wr = ep->re_max_requests;

	ep->re_attr.cap.max_recv_wr += RPCRDMA_BACKWARD_WRS;

	ep->re_attr.cap.max_recv_wr += RPCRDMA_MAX_RECV_BATCH;

	ep->re_attr.cap.max_recv_wr += ep->re_recv_batch;

	ep->re_attr.cap.max_recv_wr += 1; /* for ib_drain_rq */



	ep->re_max_rdma_segs =

net/sunrpc/xprtrdma/verbs.c

+1 −1
Original line number Diff line number Diff line
@@ -1374,7 +1374,7 @@ void rpcrdma_post_recvs(struct rpcrdma_xprt *r_xprt, int needed) 
	if (likely(ep->re_receive_count > needed))

		goto out;

	needed -= ep->re_receive_count;

	needed += RPCRDMA_MAX_RECV_BATCH;

	needed += ep->re_recv_batch;



	if (atomic_inc_return(&ep->re_receiving) > 1)

		goto out_dec;

net/sunrpc/xprtrdma/xprt_rdma.h

+1 −0
Original line number Diff line number Diff line
@@ -96,6 +96,7 @@ struct rpcrdma_ep { 
	struct rpcrdma_notification	re_rn;

	int			re_receive_count;

	unsigned int		re_max_requests; /* depends on device */

	unsigned int		re_recv_batch;

	unsigned int		re_inline_send;	/* negotiated */

	unsigned int		re_inline_recv;	/* negotiated */