On 04/26/2012 09:16 AM, Julian Stecklina wrote:
> Am Donnerstag, den 26.04.2012, 08:13 -0700 schrieb Alexander Duyck:
>> On 04/26/2012 04:39 AM, Julian Stecklina wrote:
>>> I noticed this, because interrupt throttling seems to have no effect in
>>> MSI mode or at least I am unable to limit interrupt rate using the
>>> relevant module flags or ethtool. Can anyone comment on this?
> [...]
>> I'll look into the interrupt throttling issue on MSI interrupts and get
>> back to you.  As far as I know this is supposed to be working.
> The concrete problem is that I get more then 100k IRQs per second when I
> saturate the 10G link. Shouldn't the driver automatically switch to bulk
> mode?
>
> Regards, Julian
>
The driver should be switching to polling in that case.  What kind of
traffic generator are you using to saturate the link?

Also have you tried just statically setting the ITR value using the
"ethtool -C ethX rx-usecs xxx" command?  If that works then it would
imply the issue is in the dynamic interrupt throttling logic.  I just
noticed there is a bug in the 3.3 kernel that has been fixed in 3.4 that
could be the reason for the adaptive interrupt moderation issue.  You
can find the patch on-line at http://patchwork.ozlabs.org/patch/146332/.

Please test the patch and let us know if it resolves the issue for you. 
if it does I will see if I can work with Jeff Kirsher to have us submit
it for the 3.3 stable tree to resolve this issue.

Thanks,

Alex

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