[Differential] [Request, 117 lines] D5185: tcp/lro: Allow network drivers to set the limit for TCP ACK/data segment aggregation limit

[sepherosa_gmail.com (Sepherosa Ziehau)]

sepherosa_gmail.com created this revision.
sepherosa_gmail.com added reviewers: network, adrian, delphij, royger, decui_microsoft.com, honzhan_microsoft.com, howard0su_gmail.com, gallatin, hselasky, np.
sepherosa_gmail.com added subscribers: freebsd-net-list, freebsd-virtualization-list.
Herald added a reviewer: transport.

REVISION SUMMARY
  It's append_cnt based.  Unless the network driver sets these two limits, its an NO-OP.
  
  For hn(4):
  
  - Set TCP ACK append limit to 1, i.e. aggregate 2 ACKs at most.  Aggregate anything more than 2 hurts TCP sending performance in hyperv.  This significantly improves the TCP sending performance when the number of concurrent connetion is low (2~8).  And greatly stabilize the TCP sending performance in other cases.
  - Set TCP data segments append limit to 25.  Without this limitation, hn(4) could aggregate ~45 TCP data segments for each connection (even at 64 or more connections) before dispatching them to socket code; large aggregation slows down ACK sending and eventually hurts/destabilizes TCP reception performance.  This setting stabilizes and improves TCP reception performance for >4 concurrent connections significantly.
  
  Make them sysctls so they could be adjusted.

REVISION DETAIL
  https://reviews.freebsd.org/D5185

AFFECTED FILES
  sys/dev/hyperv/netvsc/hv_net_vsc.h
  sys/dev/hyperv/netvsc/hv_netvsc_drv_freebsd.c
  sys/netinet/tcp_lro.c
  sys/netinet/tcp_lro.h

EMAIL PREFERENCES
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To: sepherosa_gmail.com, network, transport, adrian, delphij, royger, decui_microsoft.com, honzhan_microsoft.com, howard0su_gmail.com, gallatin, hselasky, np
Cc: freebsd-virtualization-list, freebsd-net-list
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