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

Jan Karcher
2022-10-24T15:47:05Z

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(-)
>