On 11 Aug 2018, at 21:06, David Miller wrote:
From: Jakub Kicinski <jakub.kicin...@netronome.com>
Date: Thu, 9 Aug 2018 20:26:08 -0700
It is not immediately clear why this is needed. The memory and
updating two sets of counters won't come for free, so perhaps a
stronger justification than troubleshooting is due? :S
Netdev has counters for fallback vs forwarded traffic, so you'd know
that traffic hits the SW datapath, plus the rules which are in_hw
will
most likely not match as of today for flower (assuming correctness).
I strongly believe that these counters are a requirement for a mixed
software/hardware (flow) based forwarding environment. The global
counters will not help much here as you might have chosen to have
certain traffic forwarded by software.
These counters are probably the only option you have to figure out why
forwarding is not as fast as expected, and you want to blame the TC
offload NIC.
I'm slightly concerned about potential performance impact, would you
be able to share some numbers for non-trivial number of flows (100k
active?)?
Agreed, features used for diagnostics cannot have a harmful penalty
for
fast path performance.
Fast path performance is not affected as these counters are not
incremented there. They are only incremented by the nic driver when they
gather their statistics from hardware.
However, the flow creation is effected, as this is where the extra
memory gets allocated. I had done some 40K flow tests before and did not
see any noticeable change in flow insertion performance. As requested by
Jakub I did it again for 100K (and threw a Netronome blade in the mix
;). I used Marcelo’s test tool,
https://github.com/marceloleitner/perf-flower.git.
Here are the numbers (time in seconds) for 10 runs in sorted order:
+-------------+----------------+
| Base_kernel | Change_applied |
+-------------+----------------+
| 5.684019 | 5.656388 |
| 5.699658 | 5.674974 |
| 5.725220 | 5.722107 |
| 5.739285 | 5.839855 |
| 5.748088 | 5.865238 |
| 5.766231 | 5.873913 |
| 5.842264 | 5.909259 |
| 5.902202 | 5.912685 |
| 5.905391 | 5.947138 |
| 6.032997 | 5.997779 |
+-------------+----------------+
I guess the deviation is in the userspace part, which is where in real
life flows get added anyway.
Let me know if more is unclear.
//Eelco
