11.0 stuck on high network load

[Slawa Olhovchenkov]

On Wed, Sep 21, 2016 at 11:25:18PM +0200, Julien Charbon wrote:

> 
>  Hi Slawa,
> 
> On 9/21/16 9:51 PM, Slawa Olhovchenkov wrote:
> > On Wed, Sep 21, 2016 at 09:11:24AM +0200, Julien Charbon wrote:
> >>  You can also use Dtrace and lockstat (especially with the lockstat -s
> >> option):
> >>
> >> https://wiki.freebsd.org/DTrace/One-Liners#Kernel_Locks
> >> https://www.freebsd.org/cgi/man.cgi?query=lockstat&manpath=FreeBSD+11.0-RELEASE
> >>
> >>  But I am less familiar with Dtrace/lockstat tools.
> > 
> > I am still use old kernel and got lockdown again.
> > Try using lockstat (I am save more output), interesting may be next:
> > 
> > R/W writer spin on writer: 190019 events in 1.070 seconds (177571 events/sec)
> > 
> > -------------------------------------------------------------------------------
> > Count indv cuml rcnt     nsec Lock                   Caller                  
> > 140839  74%  74% 0.00    24659 tcpinp                 tcp_tw_2msl_scan+0xc6   
> > 
> >       nsec ------ Time Distribution ------ count     Stack                   
> >       4096 |                               913       tcp_twstart+0xa3        
> >       8192 |@@@@@@@@@@@@                   58191     tcp_do_segment+0x201f   
> >      16384 |@@@@@@                         29594     tcp_input+0xe1c         
> >      32768 |@@@@                           23447     ip_input+0x15f          
> >      65536 |@@@                            16197     
> >     131072 |@                              8674      
> >     262144 |                               3358      
> >     524288 |                               456       
> >    1048576 |                               9         
> > -------------------------------------------------------------------------------
> > Count indv cuml rcnt     nsec Lock                   Caller                  
> > 49180  26% 100% 0.00    15929 tcpinp                 tcp_tw_2msl_scan+0xc6   
> > 
> >       nsec ------ Time Distribution ------ count     Stack                   
> >       4096 |                               157       pfslowtimo+0x54         
> >       8192 |@@@@@@@@@@@@@@@                24796     softclock_call_cc+0x179 
> >      16384 |@@@@@@                         11223     softclock+0x44          
> >      32768 |@@@@                           7426      intr_event_execute_handlers+0x95
> >      65536 |@@                             3918      
> >     131072 |                               1363      
> >     262144 |                               278       
> >     524288 |                               19        
> > -------------------------------------------------------------------------------
> 
>  This is interesting, it seems that you have two call paths competing
> for INP locks here:
> 
>  - pfslowtimo()/tcp_tw_2msl_scan(reuse=0) and
> 
>  - tcp_input()/tcp_twstart()/tcp_tw_2msl_scan(reuse=1)

I think same.

>  These paths can indeed compete for the same INP lock, as both
> tcp_tw_2msl_scan() calls always start with the first inp found in
> twq_2msl list.  But in both cases, this first inp should be quickly used
> and its lock released anyway, thus that could explain your situation it
> that the TCP stack is doing that all the time, for example:
> 
>  - Let say that you are running out completely and constantly of tcptw,
> and then all connections transitioning to TIME_WAIT state are competing
> with the TIME_WAIT timeout scan that tries to free all the expired
> tcptw.  If the stack is doing that all the time, it can appear like
> "live" locked.
> 
>  This is just an hypothesis and as usual might be a red herring.
> Anyway, could you run:
> 
> $ vmstat -z | head -2; vmstat -z | grep -E 'tcp|sock'

ITEM                   SIZE  LIMIT     USED     FREE      REQ FAIL SLEEP

socket:                 864, 4192664,   18604,   25348,49276158,   0,   0
tcp_inpcb:              464, 4192664,   34226,   18702,49250593,   0,   0
tcpcb:                 1040, 4192665,   18424,   18953,49250593,   0,   0
tcptw:                   88,  16425,   15802,     623,14526919,   8,   0
tcpreass:                40,  32800,      15,    2285,  632381,   0,   0

In normal case tcptw is about 16425/600/900

And after `sysctl -a | grep tcp` system stuck on serial console and I am reset it.

>  Ideally, once when everything is ok, and once when you have the issue
> to see the differences (if any).
> 
>  If it appears your are quite low in tcptw, and if you have enough
> memory, could you try increase the tcptw limit using sysctl

I think this is not eliminate stuck, just may do it less frequency

> net.inet.tcp.maxtcptw?  And actually see if it improve (or not) your
> performance.

I am already play with net.inet.tcp.maxtcptw and it not affect performance.