Excessive ethernet interrupts on AM335x board

[Mark Jackson]

I'm just fighting an issue with ethernet on our custom AM335x board:-

# uname -a
Linux nanobone 3.9.0-rc2-00113-gd60f039 #139 Tue Mar 12 15:14:01 GMT 2013 armv7l GNU/Linux

Every now and then, the whole unit slows to a crawl.  The only indication of any problem is:-

(a) the serial tty port becomes much less responsive
(b) normal ping times jump from 1ms to >10sec (sometimes >20sec !!)
(c) the ethernet interrupt count rockets (see below)

I've tried to force the problem by flood pinging from my PC.

# while true
> do grep "58:" /proc/interrupts; sleep 10
> done
 58:       1291      INTC  4a100000.ethernet  <<< normal pinging (about 100 irqs per 10sec)
 58:       1333      INTC  4a100000.ethernet
 58:       1372      INTC  4a100000.ethernet
 58:       3979      INTC  4a100000.ethernet  <<< start flood ping (about 4k irqs per 10sec)
 58:       6540      INTC  4a100000.ethernet
 58:      17519      INTC  4a100000.ethernet  <<< big jump >>>
 58:      20169      INTC  4a100000.ethernet
 58:      22775      INTC  4a100000.ethernet
 58:      25368      INTC  4a100000.ethernet
 58:      34598      INTC  4a100000.ethernet  <<< big jump >>>
 58:      37182      INTC  4a100000.ethernet
 58:      39730      INTC  4a100000.ethernet
 58:     141220      INTC  4a100000.ethernet  <<< whoa !!! >>>
 58:     146080      INTC  4a100000.ethernet
 58:     149351      INTC  4a100000.ethernet
 58:     152922      INTC  4a100000.ethernet
 58:     156420      INTC  4a100000.ethernet
 58:     159538      INTC  4a100000.ethernet
 58:     162711      INTC  4a100000.ethernet
 58:     165746      INTC  4a100000.ethernet
 58:     168973      INTC  4a100000.ethernet
 58:     172128      INTC  4a100000.ethernet
 58:     175030      INTC  4a100000.ethernet
 58:     177957      INTC  4a100000.ethernet
 58:     180782      INTC  4a100000.ethernet
 58:     183618      INTC  4a100000.ethernet
 58:     186450      INTC  4a100000.ethernet
 58:     189242      INTC  4a100000.ethernet
 58:     191909      INTC  4a100000.ethernet
 58:     194565      INTC  4a100000.ethernet
 58:     197153      INTC  4a100000.ethernet
 58:     199730      INTC  4a100000.ethernet  <<< another big jump >>>
 58:     252629      INTC  4a100000.ethernet
 58:     262955      INTC  4a100000.ethernet
 58:     265557      INTC  4a100000.ethernet
 58:     268131      INTC  4a100000.ethernet
 58:     272586      INTC  4a100000.ethernet
 58:     275623      INTC  4a100000.ethernet  <<< here I stop flood pings >>>
[  631.727758] nfs: server 10.0.0.100 not responding, still trying
[  638.738864] nfs: server 10.0.0.100 OK
 58:     277694      INTC  4a100000.ethernet
 58:     277703      INTC  4a100000.ethernet
 58:     277709      INTC  4a100000.ethernet
 58:     277719      INTC  4a100000.ethernet
 58:     277725      INTC  4a100000.ethernet
 58:     277734      INTC  4a100000.ethernet
 58:     277745      INTC  4a100000.ethernet

As you can see, when I stop the flood pings, the nfs link is now reported
as being lost.

Any ideas ?

Cheers
Mark J.
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