[vnet] [epair] epair interface stops working after some time

[Reshad Patuck]

Hi,

I have filed a bug for this issue and cc'd both of you in it.

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=227100

Best,

Reshad

On 29 March 2018 6:39:13 PM IST, Kristof Provost <kristof at sigsegv.be> wrote:
>On 29 Mar 2018, at 14:48, Reshad Patuck wrote:
>> pulling the 'net.link.epair.netisr_maxqlen' down does seem to make 
>> this occur faster.
>> ​
>Good, I think my hypothesis about where the issue lies is correct then.
>You should be able to avoid (or at least reduce the frequency of) the 
>issue by increasing the value on your system(s).
>
>> When I dropped it to 2 like Kristof did and I have the same symptoms 
>> on a box which was not exhibiting the problems manually began to have
>
>> the same symptoms.
>> Bumping it back up to 2100 did not restore the functionality (I don't
>
>> know if it should).
>> ​
>It’s good to know this. It doesn’t surprise me that it doesn’t fix 
>things.
>Something’s wrong in the code which handle an overflow of the netisr 
>queue in the epair driver. Once that happens the IFF_DRV_OACTIVE flag 
>gets set, and we keep enqueuing outside the netisr queue.
>Somehow we never end up back in epair_nh_drainedcpu(), so the flag
>never 
>gets cleared and the driver never recovers.
>
>> I will create a PR for this later today with all the information I 
>> have gathered so that we can have it all in one place.
>>
>Thanks. Please cc me on it. I’ll see if I can figure out what the 
>problem is, but we might need someone smarter, so cc Bjoern too.
>
>Regards,
>Kristof