Date:   Mon, 7 Nov 2022 19:05:37 +0800
From:   "D. Wythe" <alibuda@...ux.alibaba.com>
To:     Wenjia Zhang <wenjia@...ux.ibm.com>,
        Jan Karcher <jaka@...ux.ibm.com>, kgraul@...ux.ibm.com
Cc:     kuba@...nel.org, davem@...emloft.net, netdev@...r.kernel.org,
        linux-s390@...r.kernel.org, linux-rdma@...r.kernel.org
Subject: Re: [PATCH net-next v4 00/10] optimize the parallelism of SMC-R
 connections


Hi Wenjia,

Thanks a lot for your information, before that we thought you did PATCH test one by one,
now I think I have found the root cause, and I will release a new version to fix this
soon as possible.

Best Wishes.
D. Wythe

On 11/2/22 9:55 PM, Wenjia Zhang wrote:
> 
> 
> On 01.11.22 08:22, D. Wythe wrote:
>>
>> Hi Jan,
>>
>> Our team conducted some code reviews over this, but unfortunately no obvious problems were found. Hence
>> we are waiting for Tony Lu's virtual SMC-D device to test, which is expected to come in this week.  Before that,
>> I wonder if your tests are running separately on separate PATCH? If so, I would like to please you to test
>> the first PATCH and the second PATCH together. I doubt that the problem repaired by the second PATCH
>> is the cause of this issues.
>>
>> Best Wishes.
>> D. Wythe
>>
> 
> Hi D. Wythe,
> 
> We did test the series of the patches as a whole. That would be great if you could use Tony's virtual device to test SMC-D. By the way, I'll put your patches in our CI, let's see if it can find something.
> 
> Best,
> Wenjia
>>
>> On 10/24/22 9:11 PM, Jan Karcher wrote:
>>> Hi D. Wythe,
>>>
>>> I re-run the tests with your fix.
>>> SMC-R works fine now. For SMC-D we still have the following problem. It is kind of the same as i reported in v2 but even weirder:
>>>
>>> smc stats:
>>>
>>> t8345011
>>> SMC-D Connections Summary
>>>    Total connections handled          2465
>>> SMC-R Connections Summary
>>>    Total connections handled           232
>>>
>>> t8345010
>>> SMC-D Connections Summary
>>>    Total connections handled          2290
>>> SMC-R Connections Summary
>>>    Total connections handled           231
>>>
>>>
>>> smc linkgroups:
>>>
>>> t8345011
>>> [root@...45011 ~]# smcr linkgroup
>>> LG-ID    LG-Role  LG-Type  VLAN  #Conns  PNET-ID
>>> 00000400 SERV     SYM         0       0  NET25
>>> [root@...45011 ~]# smcd linkgroup
>>> LG-ID    VLAN  #Conns  PNET-ID
>>> 00000300    0      16  NET25
>>>
>>> t8345010
>>> [root@...45010 tela-kernel]# smcr linkgroup
>>> LG-ID    LG-Role  LG-Type  VLAN  #Conns  PNET-ID
>>> 00000400 CLNT     SYM         0       0  NET25
>>> [root@...45010 tela-kernel]# smcd linkgroup
>>> LG-ID    VLAN  #Conns  PNET-ID
>>> 00000300    0       1  NET25
>>>
>>>
>>> smcss:
>>>
>>> t8345011
>>> [root@...45011 ~]# smcss
>>> State          UID   Inode   Local Address           Peer Address Intf Mode
>>>
>>> t8345010
>>> [root@...45010 tela-kernel]# smcss
>>> State          UID   Inode   Local Address           Peer Address Intf Mode
>>>
>>>
>>> lsmod:
>>>
>>> t8345011
>>> [root@...45011 ~]# lsmod | grep smc
>>> smc                   225280  18 ism,smc_diag
>>> t8345010
>>> [root@...45010 tela-kernel]# lsmod | grep smc
>>> smc                   225280  3 ism,smc_diag
>>>
>>> Also smc_dbg and netstat do not show any more information on this problem. We only see in the dmesg that the code seems to build up SMC-R linkgroups even tho we are running the SMC-D tests.
>>> NOTE: we disabled the syncookies for the tests.
>>>
>>> dmesg:
>>>
>>> t8345011
>>> smc-tests: test_smcapp_torture_test started
>>> kernel: TCP: request_sock_TCP: Possible SYN flooding on port 22465. Dropping request.  Check SNMP counters.
>>> kernel: smc: SMC-R lg 00000400 net 1 link added: id 00000401, peerid 00000401, ibdev mlx5_0, ibport 1
>>> kernel: smc: SMC-R lg 00000400 net 1 state changed: SINGLE, pnetid NET25
>>> kernel: smc: SMC-R lg 00000400 net 1 link added: id 00000402, peerid 00000402, ibdev mlx5_1, ibport 1
>>> kernel: smc: SMC-R lg 00000400 net 1 state changed: SYMMETRIC, pnetid NET25
>>>
>>> t8345010
>>> smc-tests: test_smcapp_torture_test started
>>> kernel: smc: SMC-R lg 00000400 net 1 link added: id 00000401, peerid 00000401, ibdev mlx5_0, ibport 1
>>> kernel: smc: SMC-R lg 00000400 net 1 state changed: SINGLE, pnetid NET25
>>> kernel: smc: SMC-R lg 00000400 net 1 link added: id 00000402, peerid 00000402, ibdev mlx5_1, ibport 1
>>> kernel: smc: SMC-R lg 00000400 net 1 state changed: SYMMETRIC, pnetid NET25
>>>
>>> If this output does not help and if you want us to look deeper into it feel free to let us know and we can debug further.
>>>
>>> On 23/10/2022 14:43, D.Wythe wrote:
>>>> From: "D.Wythe" <alibuda@...ux.alibaba.com>
>>>>
>>>> This patch set attempts to optimize the parallelism of SMC-R connections,
>>>> mainly to reduce unnecessary blocking on locks, and to fix exceptions that
>>>> occur after thoses optimization.
>>>>
>>>> According to Off-CPU graph, SMC worker's off-CPU as that:
>>>>
>>>> smc_close_passive_work                  (1.09%)
>>>>          smcr_buf_unuse                  (1.08%)
>>>>                  smc_llc_flow_initiate   (1.02%)
>>>>
>>>> smc_listen_work                         (48.17%)
>>>>          __mutex_lock.isra.11            (47.96%)
>>>>
>>>>
>>>> An ideal SMC-R connection process should only block on the IO events
>>>> of the network, but it's quite clear that the SMC-R connection now is
>>>> queued on the lock most of the time.
>>>>
>>>> The goal of this patchset is to achieve our ideal situation where
>>>> network IO events are blocked for the majority of the connection lifetime.
>>>>
>>>> There are three big locks here:
>>>>
>>>> 1. smc_client_lgr_pending & smc_server_lgr_pending
>>>>
>>>> 2. llc_conf_mutex
>>>>
>>>> 3. rmbs_lock & sndbufs_lock
>>>>
>>>> And an implementation issue:
>>>>
>>>> 1. confirm/delete rkey msg can't be sent concurrently while
>>>> protocol allows indeed.
>>>>
>>>> Unfortunately,The above problems together affect the parallelism of
>>>> SMC-R connection. If any of them are not solved. our goal cannot
>>>> be achieved.
>>>>
>>>> After this patch set, we can get a quite ideal off-CPU graph as
>>>> following:
>>>>
>>>> smc_close_passive_work                                  (41.58%)
>>>>          smcr_buf_unuse                                  (41.57%)
>>>>                  smc_llc_do_delete_rkey                  (41.57%)
>>>>
>>>> smc_listen_work                                         (39.10%)
>>>>          smc_clc_wait_msg                                (13.18%)
>>>>                  tcp_recvmsg_locked                      (13.18)
>>>>          smc_listen_find_device                          (25.87%)
>>>>                  smcr_lgr_reg_rmbs                       (25.87%)
>>>>                          smc_llc_do_confirm_rkey         (25.87%)
>>>>
>>>> We can see that most of the waiting times are waiting for network IO
>>>> events. This also has a certain performance improvement on our
>>>> short-lived conenction wrk/nginx benchmark test:
>>>>
>>>> +--------------+------+------+-------+--------+------+--------+
>>>> |conns/qps     |c4    | c8   |  c16  |  c32   | c64  |  c200  |
>>>> +--------------+------+------+-------+--------+------+--------+
>>>> |SMC-R before  |9.7k  | 10k  |  10k  |  9.9k  | 9.1k |  8.9k  |
>>>> +--------------+------+------+-------+--------+------+--------+
>>>> |SMC-R now     |13k   | 19k  |  18k  |  16k   | 15k  |  12k   |
>>>> +--------------+------+------+-------+--------+------+--------+
>>>> |TCP           |15k   | 35k  |  51k  |  80k   | 100k |  162k  |
>>>> +--------------+------+------+-------+--------+------+--------+
>>>>
>>>> The reason why the benefit is not obvious after the number of connections
>>>> has increased dues to workqueue. If we try to change workqueue to UNBOUND,
>>>> we can obtain at least 4-5 times performance improvement, reach up to half
>>>> of TCP. However, this is not an elegant solution, the optimization of it
>>>> will be much more complicated. But in any case, we will submit relevant
>>>> optimization patches as soon as possible.
>>>>
>>>> Please note that the premise here is that the lock related problem
>>>> must be solved first, otherwise, no matter how we optimize the workqueue,
>>>> there won't be much improvement.
>>>>
>>>> Because there are a lot of related changes to the code, if you have
>>>> any questions or suggestions, please let me know.
>>>>
>>>> Thanks
>>>> D. Wythe
>>>>
>>>> v1 -> v2:
>>>>
>>>> 1. Fix panic in SMC-D scenario
>>>> 2. Fix lnkc related hashfn calculation exception, caused by operator
>>>> priority
>>>> 3. Only wake up one connection if the lnk is not active
>>>> 4. Delete obsolete unlock logic in smc_listen_work()
>>>> 5. PATCH format, do Reverse Christmas tree
>>>> 6. PATCH format, change all xxx_lnk_xxx function to xxx_link_xxx
>>>> 7. PATCH format, add correct fix tag for the patches for fixes.
>>>> 8. PATCH format, fix some spelling error
>>>> 9. PATCH format, rename slow to do_slow
>>>>
>>>> v2 -> v3:
>>>>
>>>> 1. add SMC-D support, remove the concept of link cluster since SMC-D has
>>>> no link at all. Replace it by lgr decision maker, who provides suggestions
>>>> to SMC-D and SMC-R on whether to create new link group.
>>>>
>>>> 2. Fix the corruption problem described by PATCH 'fix application
>>>> data exception' on SMC-D.
>>>>
>>>> v3 -> v4:
>>>>
>>>> 1. Fix panic caused by uninitialization map.
>>>>
>>>> D. Wythe (10):
>>>>    net/smc: remove locks smc_client_lgr_pending and
>>>>      smc_server_lgr_pending
>>>>    net/smc: fix SMC_CLC_DECL_ERR_REGRMB without smc_server_lgr_pending
>>>>    net/smc: allow confirm/delete rkey response deliver multiplex
>>>>    net/smc: make SMC_LLC_FLOW_RKEY run concurrently
>>>>    net/smc: llc_conf_mutex refactor, replace it with rw_semaphore
>>>>    net/smc: use read semaphores to reduce unnecessary blocking in
>>>>      smc_buf_create() & smcr_buf_unuse()
>>>>    net/smc: reduce unnecessary blocking in smcr_lgr_reg_rmbs()
>>>>    net/smc: replace mutex rmbs_lock and sndbufs_lock with rw_semaphore
>>>>    net/smc: Fix potential panic dues to unprotected
>>>>      smc_llc_srv_add_link()
>>>>    net/smc: fix application data exception
>>>>
>>>>   net/smc/af_smc.c   |  70 ++++----
>>>>   net/smc/smc_core.c | 478 +++++++++++++++++++++++++++++++++++++++++++++++------
>>>>   net/smc/smc_core.h |  36 +++-
>>>>   net/smc/smc_llc.c  | 277 ++++++++++++++++++++++---------
>>>>   net/smc/smc_llc.h  |   6 +
>>>>   net/smc/smc_wr.c   |  10 --
>>>>   net/smc/smc_wr.h   |  10 ++
>>>>   7 files changed, 712 insertions(+), 175 deletions(-)
>>>>

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