Re: [PATCH net-next v4 00/10] optimize the parallelism of SMC-R connections

D. Wythe
2022-11-10T09:40:05Z

Hi Wenjia,

I've found the cause of the connection leak, which is also related to failure
mentioned in my last email. Furthermore, the failure occurs on the first contact
connection, and unfortunately, our decision-maker wrongly allows SMC-D connection to
be attached to lgr before the first contact. Considering the call chain:

smc_buf_create()
ism_register_dmb() = -EINVAL

smc_conn_abort
if (local_first && lgr_valid)
smc_lgr_cleanup_early(lgr);

smc_lgr_cleanup_early
__smc_lgr_terminate
smc_conn_kill(conn, soft);
if (conn->lgr->is_smcd) {
smc_ism_unset_conn(conn);
}

smc_ism_unset_conn
conn->lgr->smcd->conn[conn->rmb_desc->sba_idx] = NULL;

As a result, the mapping of the connections on the smcd->conn is lost, and
those connections know nothing about it. They can no longer receive any messages
from ISM device, including close/abort messages.

I will fix these two problems as soon as possible by:

1. call ism_register_dmb() with lock to avoid unexpected failure.
2. force SMC-D connection to be attached to lgr after the first contact done.

D. Wythe

On 11/10/22 3:54 PM, D. Wythe wrote:
>
> Hi Wenjia,
>
> According to code in ism_register_dmb():
>
>     if (!dmb->sba_idx) {
>         bit = find_next_zero_bit(ism->sba_bitmap, ISM_NR_DMBS,
>                      ISM_DMB_BIT_OFFSET);
>         if (bit == ISM_NR_DMBS)
>             return -ENOSPC;
>
>         dmb->sba_idx = bit;
>     }
>     if (dmb->sba_idx < ISM_DMB_BIT_OFFSET ||
>         test_and_set_bit(dmb->sba_idx, ism->sba_bitmap))
>         return -EINVAL;
>
> We can see that ism_register_dmb() is not thread-safe, invoking this function at the same time
> without protected may fail with -EINVAL (different callers might get the same bit on
> find_next_zero_bit()).
>
> Considering the stack call chain:
>
> smc_listen_work
>
> smc_listen_find_device
>     smc_find_ism_v2_device_serv()
>     if (ini->dev[0])
>         return
>     smc_find_ism_v1_device_serv()
>     if (ini->dev[0])
>         return
>     smc_find_rdma_v2_device_serv()
>
> smc_find_ism_v2_device_serv:
>
>     /* separate - outside the smcd_dev_list.lock */
>     smcd_version = ini->smcd_version;
>     for (i = 0; i < matches; i++) {
>         ini->smcd_version = SMC_V2;
>         ini->is_smcd = true;
>         ini->ism_selected = i;
>         rc = smc_listen_ism_init(new_smc, ini);
>         if (rc) {
>             smc_find_ism_store_rc(rc, ini);
>             /* try next active ISM device */
>             continue;
>         }
>         return; /* matching and usable V2 ISM device found */
>     }
>     /* no V2 ISM device could be initialized */
>     ini->smcd_version = smcd_version;    /* restore original value */
>     ini->negotiated_eid[0] = 0;
>
> not_found:
>     ini->smcd_version &= ~SMC_V2;
>     ini->ism_dev[0] = NULL;
>     ini->is_smcd = false;
>
>
> smc_listen_ism_init
> smc_buf_create
> __smc_buf_create
> smcd_new_buf_create(is_rmb = true)
>
> smc_ism_register_dmb
>     return -EINVAL;
>
>
> Therefore, the failure of ism_register_dmb() will result in smc_find_ism_v2_device_serv() failed,
> Similarly, smc_find_ism_v1_device_serv() may also fail too, then SMC-R is finally selected.
> If my guess is correct, the SMC-D connections should include different versions of v1 and v2 if
> v1&v2 are both supplied. (you could see it by $(smcr -dd stats))
>
>
> However, the leak problem of connection cannot be explained.
> Could you help me dump the status of those connection, I wish to
> know which state they stayed at last. (crash utils or $(smcr -a))
>
>
> Thanks.
> D. Wythe
>
>
> On 11/10/22 1:31 AM, Wenjia Zhang wrote:
>>
>>
>> On 09.11.22 10:10, D. Wythe wrote:
>>>
>>> Hi Wenjia and Jan,
>>>
>>> I'm not sure whether my guess is right, I need some help from you. I guess the smcd_ops register_dmb()
>>> is not thread-safe, after I remove the lock, different connections might get the same sba_idx, which will cause
>>> the connection to be lost in the map(smcd->conn). If so, the CDC message carrying close/abort information cannot be
>>> distributed to the correct connection, then the connection remains in link group abnormally.
>>>
>>> /* Set a connection using this DMBE. */
>>> void smc_ism_set_conn(struct smc_connection *conn)
>>> {
>>>      unsigned long flags;
>>>
>>>      spin_lock_irqsave(&conn->lgr->smcd->lock, flags);
>>>      conn->lgr->smcd->conn[conn->rmb_desc->sba_idx] = conn;
>>>      spin_unlock_irqrestore(&conn->lgr->smcd->lock, flags);
>>> }
>>>
>>>
>>> struct smcd_ops {
>>>
>>>      int (*register_dmb)(struct smcd_dev *dev, struct smcd_dmb *dmb);
>>> }
>>>
>>>
>>
>> Hi D. Wythe,
>>
>> Very glad if we can help. It does look very questionable. However, I don't really think it's the reason to trigger the problem. I did some traces, and saw there was already something wrong during the CLC handshake, where one connection is decided for SMC-R not -D. This is one piece of the snapshot of the trace:
>>
>> <...>-540539 [000] 306429.068196::|  smc_connect() {
>> <...>-540539 [000] 306429.068198::|    smc_copy_sock_settings_to_clc();
>> <...>-540539 [000] 306429.120310::|    smc_ism_is_v2_capable();
>> <...>-540539 [000] 306429.120316::|    .LASANPC6743();
>> <...>-540539 [000] 306429.120319::|    smc_find_proposal_devices() {
>> <...>-540539 [000] 306429.120319::|      smc_pnet_find_ism_resource() {
>> <...>-540539 [000] 306429.120331::|        smc_pnet_match();
>> <...>-540539 [000] 306429.120332::|      }
>> <...>-540539 [000] 306429.120333::|      smc_ism_get_chid();
>> <...>-540539 [000] 306429.120334::|      smc_pnet_find_roce_resource() {
>> <...>-540539 [000] 306429.120344::|        smc_pnet_match();
>> <...>-540539 [000] 306429.120346::|        smc_ib_port_active();
>> <...>-540539 [000] 306429.120347::|        smc_pnet_determine_gid() {
>> <...>-540539 [000] 306429.120347::|          smc_ib_determine_gid() {
>> <...>-540539 [000] 306429.120350::|            smc_ib_determine_gid_rcu();
>> <...>-540539 [000] 306429.120351::|          }
>> <...>-540539 [000] 306429.120352::|        }
>> <...>-540539 [000] 306429.120352::|      }
>> <...>-540539 [000] 306429.120353::|      smc_ism_is_v2_capable();
>> <...>-540539 [000] 306429.120355::|      smc_clc_ueid_count();
>> <...>-540539 [000] 306429.120357::|      smc_pnet_find_roce_resource() {
>> <...>-540539 [000] 306429.120367::|        smc_pnet_match();
>> <...>-540539 [000] 306429.120368::|        smc_ib_port_active();
>> <...>-540539 [000] 306429.120369::|        smc_pnet_determine_gid() {
>> <...>-540539 [000] 306429.120370::|          smc_ib_determine_gid() {
>> <...>-540539 [000] 306429.120372::|            smc_ib_determine_gid_rcu();
>> <...>-540539 [000] 306429.120376::|            smc_ib_determine_gid_rcu();
>> <...>-540539 [000] 306429.120379::|            smc_ib_determine_gid_rcu();
>> <...>-540539 [000] 306429.120382::|            smc_ib_determine_gid_rcu();
>> <...>-540539 [000] 306429.120650::|          }
>> <...>-540539 [000] 306429.120651::|        }
>> <...>-540539 [000] 306429.120652::|        smc_pnet_match();
>> <...>-540539 [000] 306429.120653::|        smc_ib_port_active();
>> <...>-540539 [000] 306429.120654::|        smc_pnet_determine_gid() {
>> <...>-540539 [000] 306429.120654::|          smc_ib_determine_gid() {
>> <...>-540539 [000] 306429.120657::|            smc_ib_determine_gid_rcu();
>> <...>-540539 [000] 306429.120660::|            smc_ib_determine_gid_rcu();
>> <...>-540539 [000] 306429.120829::|          }
>> <...>-540539 [000] 306429.120829::|        }
>> <...>-540539 [000] 306429.120830::|      }
>> <...>-540539 [000] 306429.120831::|    }
>> <...>-540539 [000] 306429.120836::|    .LASANPC6660() {
>> <...>-540539 [000] 306429.120843::|      .LASANPC6654() {
>> <...>-540539 [000] 306429.120847::|        smc_clc_prfx_set4_rcu.isra.0();
>> <...>-540539 [000] 306429.120849::|      }
>> <...>-540539 [000] 306429.120850::|      smc_ism_get_chid();
>> <...>-540539 [000] 306429.120851::|      smc_ism_get_system_eid();
>> <...>-540539 [000] 306429.120889::|    }
>> <...>-540539 [000] 306429.120890::|    .LASANPC6658() {
>> <...>-540539 [000] 306429.124906::|      smc_clc_msg_hdr_valid();
>> <...>-540539 [000] 306429.124908::|    }
>> <...>-540539 [000] 306429.124908::|    .LASANPC6727() {
>> <...>-540539 [000] 306429.124909::|      smc_connect_rdma_v2_prepare();
>> <...>-540539 [000] 306429.124912::|      smc_conn_create() {
>>
>>> On 11/7/22 7:05 PM, D. Wythe wrote:
>>>>
>>>> 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@t8345011 ~]# smcr linkgroup
>>>>>>> LG-ID    LG-Role  LG-Type  VLAN  #Conns  PNET-ID
>>>>>>> 00000400 SERV     SYM         0       0  NET25
>>>>>>> [root@t8345011 ~]# smcd linkgroup
>>>>>>> LG-ID    VLAN  #Conns  PNET-ID
>>>>>>> 00000300    0      16  NET25
>>>>>>>
>>>>>>> t8345010
>>>>>>> [root@t8345010 tela-kernel]# smcr linkgroup
>>>>>>> LG-ID    LG-Role  LG-Type  VLAN  #Conns  PNET-ID
>>>>>>> 00000400 CLNT     SYM         0       0  NET25
>>>>>>> [root@t8345010 tela-kernel]# smcd linkgroup
>>>>>>> LG-ID    VLAN  #Conns  PNET-ID
>>>>>>> 00000300    0       1  NET25
>>>>>>>
>>>>>>>
>>>>>>> smcss:
>>>>>>>
>>>>>>> t8345011
>>>>>>> [root@t8345011 ~]# smcss
>>>>>>> State          UID   Inode   Local Address           Peer Address Intf Mode
>>>>>>>
>>>>>>> t8345010
>>>>>>> [root@t8345010 tela-kernel]# smcss
>>>>>>> State          UID   Inode   Local Address           Peer Address Intf Mode
>>>>>>>
>>>>>>>
>>>>>>> lsmod:
>>>>>>>
>>>>>>> t8345011
>>>>>>> [root@t8345011 ~]# lsmod | grep smc
>>>>>>> smc                   225280  18 ism,smc_diag
>>>>>>> t8345010
>>>>>>> [root@t8345010 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@linux.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(-)
>>>>>>>>