netisr process eats 100% cpu

[hiren panchasara]

On 09/11/15 at 12:46P, Dmitry Sivachenko wrote:
> 
> > 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.
>

I am not sure what keep cpu busy with netisr when localhost is involved.

You may want to post o/p of 
# sysctl net.isr
# netstat -Q
# sysctl net.inet | grep queue

A suggestion I see at https://calomel.org/freebsd_network_tuning.html is
to increase localhost n/w buffers. Not sure if this'll help your case.
net.local.stream.sendspace=164240  # (default 8192)
net.local.stream.recvspace=164240  # (default 8192)

Now I'll let someone else with more ideas/clues comment.

Cheers,
Hiren
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