Merge branch 'smc-optimizations'

Merge branch 'smc-optimizations'

D. Wythe says:

====================
net/smc: Optimizing performance in short-lived scenarios

This patch set aims to optimizing performance of SMC in short-lived
links scenarios, which is quite unsatisfactory right now.

In our benchmark, we test it with follow scripts:

./wrk -c 10000 -t 4 -H 'Connection: Close' -d 20 http://smc-server

Current performance figures like that:

Running 20s test @ http://11.213.45.6
  4 threads and 10000 connections
  4956 requests in 20.06s, 3.24MB read
  Socket errors: connect 0, read 0, write 672, timeout 0
Requests/sec:    247.07
Transfer/sec:    165.28KB

There are many reasons for this phenomenon, this patch set doesn't
solve it all though, but it can be well alleviated with it in.

Patch 1/5  (Make smc_tcp_listen_work() independent) :

Separate smc_tcp_listen_work() from smc_listen_work(), make them
independent of each other, the busy SMC handshake can not affect new TCP
connections visit any more. Avoid discarding a large number of TCP
connections after being overstock, which is undoubtedly raise the
connection establishment time.

Patch 2/5 (Limit SMC backlog connections):

Since patch 1 has separated smc_tcp_listen_work() from
smc_listen_work(), an unrestricted TCP accept have come into being. This
patch try to put a limit on SMC backlog connections refers to
implementation of TCP.

Patch 3/5 (Limit SMC visits when handshake workqueue congested):

Considering the complexity of SMC handshake right now, in short-lived
links scenarios, this may not be the main scenario of SMC though, it's
performance is still quite poor. This patch try to provide constraint on
SMC handshake when handshake workqueue congested, which is the sign of
SMC handshake stacking in our opinion.

Patch 4/5 (Dynamic control handshake limitation by socket options)

This patch allow applications dynamically control the ability of SMC
handshake limitation. Since SMC don't support set SMC socket option
before,
this patch also have to support SMC's owns socket options.

Patch 5/5 (Add global configure for handshake limitation by netlink)

This patch provides a way to get benefit of handshake limitation
without
modifying any code for applications, which is quite useful for most
existing applications.

After this patch set, performance figures like that:

Running 20s test @ http://11.213.45.6
  4 threads and 10000 connections
  693253 requests in 20.10s, 452.88MB read
Requests/sec:  34488.13
Transfer/sec:     22.53MB

That's a quite well performance improvement, about to 6 to 7 times in my
environment.
---
changelog:
v1 -> v2:
- fix compile warning
- fix invalid dependencies in kconfig
v2 -> v3:
- correct spelling mistakes
- fix useless variable declare
v3 -> v4
- make smc_tcp_ls_wq be static
v4 -> v5
- add dynamic control for SMC auto fallback by socket options
- add global configure for SMC auto fallback through netlink
v5 -> v6
- move auto fallback to net namespace scope
- remove auto fallback attribute in SMC_GEN_SYS_INFO
- add independent attributes for auto fallback
v6 -> v7
- fix wording and the naming issues, rename 'auto fallback' to handshake
  limitation.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>