@@ -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:
@@ -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 @@
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;
@@ -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;
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> --- Hi Tejun- I'm interested in your comments about how rpcrdma_reply_handler uses queue_work to spread workload away from the CPU core that is assigned to handle Receive completions, in particular how it might work on NUMA systems. The rpcrdma_receive_wq workqueue is no longer WQ_UNBOUND. In this patch I have changed the mechanism from queuing work on a particular core to queuing work using WORK_CPU_UNBOUND and letting the scheduler choose where the work item is dispatched. The purpose is to move work away from the Receiving CPU when it is busy, to help the workload scale well on systems with multiple CPUs. 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(-) -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html