Re: [PATCH net-next v3 00/10] optimize the parallelism of SMC-R connections

D. Wythe
2022-10-20T07:01:05Z

Hi Jan,

Sorry for the long delay, The main purpose of v3 is to put optimizes also works on SMC-D, dues to the environment,
I can only tests it in SMC-R, so please help us to verify the stability and functional in SMC-D,
Thanks a lot.

If you have any problems, please let us know.

Besides, PATCH bug fixes need to be reordered. After the code review passes and the SMC-D test goes stable, I will adjust it
in next serial.

On 10/20/22 2:43 PM, 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.
>
> 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(-)
>