netisr process eats 100% cpu

[Dmitry Sivachenko]

> hiren panchasara <hiren at strugglingcoder.info> wrote:
> 
> Unsure at the moment if loopback is causing the trouble for you or not.
> See:

(please keep me CC'ed, I am not subscribed to -net)


>
> https://lists.freebsd.org/pipermail/freebsd-net/2015-February/041239.html
>
>

Yes, this thread looks similar.


> You may want to try:
> 1) pmcstat and see if you can catch something

What particular should I look for?  Here is first lines of pmcstat -T -S instructions -w 1:
PMC: [INSTR_RETIRED_ANY] Samples: 157198 (100.0%) , 0 unresolved

%SAMP IMAGE      FUNCTION             CALLERS
 13.2 kernel     cpu_search_highest   cpu_search_highest:12.0 sched_idletd:1.2
  8.3 kernel     ipfw_chk             ipfw_check_packet
  3.1 myprogram   memsetAVX            _ZN12TLz4Compress7DoWriteEPKv
  2.3 kernel     tcp_output           tcp_usr_send:1.0 tcp_do_segment:0.9


> 2) disable checksum on localhost


I tried, but nothing has changed.


> 3) look at netisr settings. sysctl net.isr o/p and how it looks under
> netstat -Q. I am not sure if adding more threads to netisr via


What should I look for?


> net.isr.numthreads would help. (Note its a loader.conf variable)


This netisr load looks parasitical to me (as I noted, moving haproxy to a separate machine does not burn CPU cycles on netisr, why is localhost special?)

Even if adding more threads to netisr would boost network utilization, wouldn't those CPU cycles spent for netisr just be a waste of energy?  I have other tasks for these CPU.


>
> As I said, I am not sure whats up. Just throwing some ideas here.


Thanks!