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Date: Fri, 19 Apr 2024 08:15:20 -0700
From: Stephen Hemminger <stephen@networkplumber.org>
To: chuck.lever@oracle.com, trond.myklebust@hammerspace.com,
 anna@kernel.org, jlayton@kernel.org, neilb@suse.de, kolga@netapp.com,
 Dai.Ngo@oracle.com, tom@talpey.com
Cc: linux-nfs@vger.kernel.org
Subject: Fw: [Bug 218743] New: NFS-RDMA-Connected Regression Found on
 Upstream Linux 6.9-rc1
Message-ID: <20240419081520.57bf66c1@hermes.local>
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I forward networking bugs to the maintainers.
Netdev does not use bugzilla, not sure if NFS does.

Begin forwarded message:

Date: Thu, 18 Apr 2024 00:00:22 +0000
From: bugzilla-daemon@kernel.org
To: stephen@networkplumber.org
Subject: [Bug 218743] New: NFS-RDMA-Connected Regression Found on Upstream Linux 6.9-rc1


https://bugzilla.kernel.org/show_bug.cgi?id=218743

            Bug ID: 218743
           Summary: NFS-RDMA-Connected Regression Found on Upstream Linux
                    6.9-rc1
           Product: Networking
           Version: 2.5
    Kernel Version: 6.9-rc1
          Hardware: Intel
                OS: Linux
            Status: NEW
          Severity: high
          Priority: P3
         Component: Other
          Assignee: stephen@networkplumber.org
          Reporter: manuel.gomez@cornelisnetworks.com
                CC: dennis.dalessandro@cornelisnetworks.com
        Regression: Yes
           Bisected e084ee673c77cade06ab4c2e36b5624c82608b8c
         commit-id:

On the Linux 6.9-rc1 kernel there is a performance regression for NFS file
transfers when Connected IPoIB mode is enabled. The network switch is OPA
(Omnipath Architecture).

The most recent good commit in my bisection was the v6.8 mainline kernel
(e8f897f4afef0031fe618a8e94127a0934896aba). Bisecting from v6.8 to v6.9-rc1
showed me that "[e084ee673c77cade06ab4c2e36b5624c82608b8c] svcrdma: Add Write
chunk WRs to the RPC's Send WR chain" was indeed the culprit of the regression.


Here are the steps I ran to reproduce the issue:
1. Establish IPoIB Connected Mode on both client and host nodes:
"echo connected > /sys/class/net/ibs785/mode"


2. Start an NFS server on the host node:
"systemctl start opafm
sleep 10
systemctl start nfs-server
modprobe svcrdma
echo "rdma 20049" > /proc/fs/nfsd/portlist
mkdir -p /mnt/nfs_test
mount -t tmpfs -o size=4096M tmpfs /mnt/nfs_test
sudo exportfs -o fsid=0,rw,async,insecure,no_root_squash
192.168.2.0/255.255.255.0:/mnt/nfs_test_testrun/"


3. Ready the client node:
"mkdir -p /mnt/nfs_test
mount -o rdma,port=20049 192.168.2.1:/mnt/nfs_test_testrun
/mnt/nfs_test_testrun/"


4. Run the actual test from the client node:
"
#!/bin/bash

fsize=268435456
jfile=/dev/shm/run_nfs_test2.junk
tfile=/dev/shm/run_nfs_test2.tmp
nfsfile=/mnt/nfs_test_testrun/run_nfs_test2.junk
rm -r -f /mnt/nfs_test_testrun/
rm -f ${tfile}
rm -f ${jfile}

dd if=/dev/urandom iflag=fullblock of=${jfile} bs=1024 count=$((fsize/1024));

for i in {1..100}; do
          cp ${jfile} ${nfsfile}; # Bottleneck 1

          cp ${nfsfile} ${tfile}; # Bottleneck 2

         cmp ${jfile} ${tfile};

          rm -f ${tfile};
        echo "DONE with iter ${i}"
done;

rm -f ${jfile};
rm -f ${tfile};
echo "Done";
"


On v6.8 I was seeing this test taking about 1m50s to complete, for all 10
iterations. On v6.9-rc1 it takes 3-7 minutes, and I also see these kernel
traces printed continuously in dmesg during this regression:

[23720.243905] INFO: task kworker/61:1:556 blocked for more than 122 seconds.
[23720.251709]       Not tainted 6.9.0-rc1 #1
[23720.256387] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this
message.
[23720.265268] task:kworker/61:1    state:D stack:0     pid:556   tgid:556  
ppid:2      flags:0x00004000
[23720.275822] Workqueue: events __svc_rdma_free [rpcrdma]
[23720.281803] Call Trace:
[23720.284630]  <TASK>
[23720.287067]  __schedule+0x210/0x660
[23720.291063]  schedule+0x2c/0xb0
[23720.294668]  schedule_timeout+0x146/0x160
[23720.299249]  __wait_for_common+0x92/0x1d0
[23720.303828]  ? __pfx_schedule_timeout+0x10/0x10
[23720.308987]  __ib_drain_sq+0xfa/0x170 [ib_core]
[23720.314190]  ? __pfx_ib_drain_qp_done+0x10/0x10 [ib_core]
[23720.320343]  ib_drain_qp+0x71/0x80 [ib_core]
[23720.325232]  __svc_rdma_free+0x28/0x100 [rpcrdma]
[23720.330604]  process_one_work+0x196/0x3d0
[23720.335185]  worker_thread+0x2fc/0x410
[23720.339470]  ? __pfx_worker_thread+0x10/0x10
[23720.344336]  kthread+0xdf/0x110
[23720.347941]  ? __pfx_kthread+0x10/0x10
[23720.352225]  ret_from_fork+0x30/0x50
[23720.356317]  ? __pfx_kthread+0x10/0x10
[23720.360602]  ret_from_fork_asm+0x1a/0x30
[23720.365083]  </TASK>

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