From: Chuck Lever Date: Fri, 6 Mar 2026 21:56:27 +0000 (-0500) Subject: xprtrdma: Scale receive batch size with credit window X-Git-Tag: v7.1-rc1~12^2~11 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=93b4791adb1017b2b079b4a453e7159e101a7e55;p=thirdparty%2Fkernel%2Flinux.git 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: Chuck Lever Signed-off-by: Trond Myklebust --- diff --git a/net/sunrpc/xprtrdma/frwr_ops.c b/net/sunrpc/xprtrdma/frwr_ops.c index 229057d35fb8..7f79a0a2601e 100644 --- a/net/sunrpc/xprtrdma/frwr_ops.c +++ b/net/sunrpc/xprtrdma/frwr_ops.c @@ -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 = diff --git a/net/sunrpc/xprtrdma/verbs.c b/net/sunrpc/xprtrdma/verbs.c index 90fd83f2d846..aecf9c0a153f 100644 --- a/net/sunrpc/xprtrdma/verbs.c +++ b/net/sunrpc/xprtrdma/verbs.c @@ -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; diff --git a/net/sunrpc/xprtrdma/xprt_rdma.h b/net/sunrpc/xprtrdma/xprt_rdma.h index 37bba72065e8..f53a77472724 100644 --- a/net/sunrpc/xprtrdma/xprt_rdma.h +++ b/net/sunrpc/xprtrdma/xprt_rdma.h @@ -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 */