Return-Path: Received: from mail-io0-f194.google.com ([209.85.223.194]:35340 "EHLO mail-io0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934322AbeB1Uaa (ORCPT ); Wed, 28 Feb 2018 15:30:30 -0500 Subject: [PATCH 1/8] xprtrdma: Fix latency regression on NUMA NFS/RDMA clients From: Chuck Lever To: anna.schumaker@netapp.com Cc: linux-rdma@vger.kernel.org, linux-nfs@vger.kernel.org Date: Wed, 28 Feb 2018 15:30:27 -0500 Message-ID: <20180228203027.25968.44687.stgit@manet.1015granger.net> In-Reply-To: <20180228202916.25968.21750.stgit@manet.1015granger.net> References: <20180228202916.25968.21750.stgit@manet.1015granger.net> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Sender: linux-nfs-owner@vger.kernel.org List-ID: With v4.15, on one of my NFS/RDMA clients I measured a nearly doubling in the latency of small read and write system calls. There was no change in server round trip time. The extra latency appears in the whole RPC execution path. "git bisect" settled on commit ccede7598588 ("xprtrdma: Spread reply processing over more CPUs") . After some experimentation, I found that leaving the WQ bound and allowing the scheduler to pick the dispatch CPU seems to eliminate the long latencies, and it does not introduce any new regressions. The fix is implemented by reverting only the part of commit ccede7598588 ("xprtrdma: Spread reply processing over more CPUs") that dispatches RPC replies specifically on the CPU where the matching RPC call was made. Interestingly, saving the CPU number and later queuing reply processing there was effective _only_ for a NFS READ and WRITE request. On my NUMA client, in-kernel RPC reply processing for asynchronous RPCs was dispatched on the same CPU where the RPC call was made, as expected. However synchronous RPCs seem to get their reply dispatched on some other CPU than where the call was placed, every time. Fixes: ccede7598588 ("xprtrdma: Spread reply processing over ... ") Signed-off-by: Chuck Lever --- net/sunrpc/xprtrdma/rpc_rdma.c | 2 +- net/sunrpc/xprtrdma/transport.c | 2 -- net/sunrpc/xprtrdma/xprt_rdma.h | 1 - 3 files changed, 1 insertion(+), 4 deletions(-) diff --git a/net/sunrpc/xprtrdma/rpc_rdma.c b/net/sunrpc/xprtrdma/rpc_rdma.c index f0855a9..4bc0f4d 100644 --- a/net/sunrpc/xprtrdma/rpc_rdma.c +++ b/net/sunrpc/xprtrdma/rpc_rdma.c @@ -1366,7 +1366,7 @@ void rpcrdma_reply_handler(struct rpcrdma_rep *rep) trace_xprtrdma_reply(rqst->rq_task, rep, req, credits); - queue_work_on(req->rl_cpu, rpcrdma_receive_wq, &rep->rr_work); + queue_work(rpcrdma_receive_wq, &rep->rr_work); return; out_badstatus: diff --git a/net/sunrpc/xprtrdma/transport.c b/net/sunrpc/xprtrdma/transport.c index 4b1ecfe..f86021e 100644 --- a/net/sunrpc/xprtrdma/transport.c +++ b/net/sunrpc/xprtrdma/transport.c @@ -52,7 +52,6 @@ #include #include #include -#include #include "xprt_rdma.h" @@ -651,7 +650,6 @@ if (!rpcrdma_get_recvbuf(r_xprt, req, rqst->rq_rcvsize, flags)) goto out_fail; - req->rl_cpu = smp_processor_id(); req->rl_connect_cookie = 0; /* our reserved value */ rpcrdma_set_xprtdata(rqst, req); rqst->rq_buffer = req->rl_sendbuf->rg_base; diff --git a/net/sunrpc/xprtrdma/xprt_rdma.h b/net/sunrpc/xprtrdma/xprt_rdma.h index 69883a9..430a6de 100644 --- a/net/sunrpc/xprtrdma/xprt_rdma.h +++ b/net/sunrpc/xprtrdma/xprt_rdma.h @@ -334,7 +334,6 @@ enum { struct rpcrdma_buffer; struct rpcrdma_req { struct list_head rl_list; - int rl_cpu; unsigned int rl_connect_cookie; struct rpcrdma_buffer *rl_buffer; struct rpcrdma_rep *rl_reply;