problems with e1000 and flow control

problems with e1000 and flow control

[Wolfgang Walter]

Hello,

it seems that e1000 enables flow-control (rx pause frames) even if the switch 
does not advertise flow control. This seems to get a problem as (at least 
some) switches then forward pause frames directed to the card from other 
hosts. We think there are hosts which indeed do this in the lans of our 
student halls.

I think flow control should be completely disabled by default if the switch 
does not advertise it. It still can be forced with ethtool.

Regards,
-- 
Wolfgang Walter
Studentenwerk München
Anstalt des öffentlichen Rechts

RE: problems with e1000 and flow control

[Brandeburg, Jesse]

Wolfgang Walter wrote:
> it seems that e1000 enables flow-control (rx pause frames) even if
> the switch does not advertise flow control. This seems to get a
> problem as (at least some) switches then forward pause frames
> directed to the card from other hosts. We think there are hosts which
> indeed do this in the lans of our student halls.
> 
> I think flow control should be completely disabled by default if the
> switch does not advertise it. It still can be forced with ethtool.

We agree, and our latest standalone drivers have taken this into
account, but the kernel drivers have not been updated all the way yet to
fix this issue.

Thanks for the input, 
 Jesse

Re: problems with e1000 and flow control

[Kok, Auke]

Wolfgang Walter wrote:
> Hello,
> 
> it seems that e1000 enables flow-control (rx pause frames) even if the switch 
> does not advertise flow control. This seems to get a problem as (at least 
> some) switches then forward pause frames directed to the card from other 
> hosts. We think there are hosts which indeed do this in the lans of our 
> student halls.
> 
> I think flow control should be completely disabled by default if the switch 
> does not advertise it. It still can be forced with ethtool.

Are you sure that the switch actually advertises the flow control "disabled"
setting properly? Perhaps you can include the e1000 ethtool flow control settings
and dmesg output (2.6.24 will print out FC status when link comes up).

There's a lengthy argumentation including spec references in the e1000/e1000e
driver code on how FC is handled (look for "IEEE 802.3ab"). Can you take a look at
that and see what might be happening?

Changing this behaviour might give other people issues which is something we need
to be very cautious about, obviously :)

Cheers,

Auke

Re: problems with e1000 and flow control

[Kok, Auke]

Brandeburg, Jesse wrote:
> Wolfgang Walter wrote:
>> it seems that e1000 enables flow-control (rx pause frames) even if
>> the switch does not advertise flow control. This seems to get a
>> problem as (at least some) switches then forward pause frames
>> directed to the card from other hosts. We think there are hosts which
>> indeed do this in the lans of our student halls.
>>
>> I think flow control should be completely disabled by default if the
>> switch does not advertise it. It still can be forced with ethtool.
> 
> We agree, and our latest standalone drivers have taken this into
> account, but the kernel drivers have not been updated all the way yet to
> fix this issue.

ok, that explains what is going on :)

I'll take a look into getting these changes upstream. Perhaps Wolfgang can confirm
that the driver on e1000.sf.net is properly working for him?

Auke

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