2012/5/30 Jean-Michel Hautbois [off-list ref]:

2012/5/30  [off-list ref]:

quoted

quoted

-----Original Message-----
From: netdev-owner@vger.kernel.org [mailto:netdev-owner@vger.kernel.org] On
Behalf Of Jean-Michel Hautbois

2012/5/30 Jean-Michel Hautbois [off-list ref]:

I used vmstat in order to see the differences between the two kernels.
The main difference is the number of interrupts per second.
I have an average of 87500 on 3.2 and 7500 on 2.6, 10 times lower !
I suspect the be2net driver to be the main cause, and I checkes the
/proc/interrupts file in order to be sure.

I have for eth1-tx on 2.6.26 about 2200 interrupts per second and 23000 on 3.2.
BTW, it is named eth1-q0 on 3.2 (and tx and rx are the same IRQ)
whereas there is eth1-rx0 and eth1-tx on 2.6.26.

Yes, there is an issue with be2net interrupt mitigation in the recent code with
RX and TX on the same Evt-Q (commit 10ef9ab4). The high interrupt rate happens when a TX blast is
done while RX is relatively silent on a queue pair. Interrupt rate due to TX completions is not being
mitigated.

I have a fix and will send it out soon..

thanks,
-Sathya

Hi Sathya !
Thanks for this information !
I had the correct diagnostic :). I am waiting for your fix.

Well, well, well, after having tested several configurations, several
drivers, I have a big difference between an old 2.6.26 kernel and a
newer one (I tried 3.2 and 3.4).

Here is my stream : UDP packets (multicast), 4000 bytes length, MTU
set to 4096. I am sending packets only, nothing on RX.
I send from 1Gbps upto 2.4Gbps and I see no drops in tc with 2.6.26
kernel, but a lot of drops with a newer kernel.
So, I don't know if I missed something in my kernel configuration, but
I have used the 2.6.26 one as a reference, in order to set the same
options (DMA related, etc).

I easily reproduce this problem and setting a bigger txqueuelen solves
it partially.
1Gbps requires a txqueulen of 9000, 2.4Gbps requires more than 20000 !

If you have any idea, I am interested, as this is a big issue for my use case.

JM