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

D. Wythe
2022-11-10T07:55:11Z

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(-)
>>>>>>>