4.16-stable review patch. If anyone has any objections, please let me know.
------------------
From: Chuck Lever chuck.lever@oracle.com
commit 6720a89933739cb8dec748cd253f7c8df2c0ae4d upstream.
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 chuck.lever@oracle.com Cc: stable@vger.kernel.org # v4.15+ Signed-off-by: Anna Schumaker Anna.Schumaker@Netapp.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- 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(-)
--- a/net/sunrpc/xprtrdma/rpc_rdma.c +++ b/net/sunrpc/xprtrdma/rpc_rdma.c @@ -1366,7 +1366,7 @@ void rpcrdma_reply_handler(struct rpcrdm
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: --- a/net/sunrpc/xprtrdma/transport.c +++ b/net/sunrpc/xprtrdma/transport.c @@ -52,7 +52,6 @@ #include <linux/slab.h> #include <linux/seq_file.h> #include <linux/sunrpc/addr.h> -#include <linux/smp.h>
#include "xprt_rdma.h"
@@ -651,7 +650,6 @@ xprt_rdma_allocate(struct rpc_task *task 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; --- 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;