Re: CPU scheduler to TXQ binding? (ixgbe vs. igb)

On Wed, 17 Sep 2014 07:59:51 -0700
Alexander Duyck [off-list ref] wrote:

On 09/17/2014 07:32 AM, Eric Dumazet wrote:

quoted

On Wed, 2014-09-17 at 15:26 +0200, Jesper Dangaard Brouer wrote:

quoted

The CPU to TXQ binding behavior of ixgbe vs. igb NIC driver are
somehow different.  Normally I setup NIC IRQ-to-CPU bindings 1-to-1,
with script set_irq_affinity [1].

For forcing use of a specific HW TXQ, I normally force the CPU binding
of the process, either with "taskset" or with "netperf -T lcpu,rcpu".

This works fine with driver ixgbe, but not with driver igb.  That is
with igb, the program forced to specific CPU, can still use another
TXQ. What am I missing?


I'm monitoring this with both:
 1) watch -d sudo tc -s -d q ls dev ethXX
 2) https://github.com/ffainelli/bqlmon

[1] https://github.com/netoptimizer/network-testing/blob/master/bin/set_irq_affinity

Have you setup XPS ?

echo 0001 >/sys/class/net/ethX/queues/tx-0/xps_cpus
echo 0002 >/sys/class/net/ethX/queues/tx-1/xps_cpus
echo 0004 >/sys/class/net/ethX/queues/tx-2/xps_cpus
echo 0008 >/sys/class/net/ethX/queues/tx-3/xps_cpus
echo 0010 >/sys/class/net/ethX/queues/tx-4/xps_cpus
echo 0020 >/sys/class/net/ethX/queues/tx-5/xps_cpus
echo 0040 >/sys/class/net/ethX/queues/tx-6/xps_cpus
echo 0080 >/sys/class/net/ethX/queues/tx-7/xps_cpus

Or something like that, depending on number of cpus and TX queues.

That was what I was thinking as well.

ixgbe has ATR which makes use of XPS to setup the transmit queues for a
1:1 mapping.  The receive side of the flow is routed back to the same Rx
queue through flow director mappings.

In the case of igb it only has RSS and doesn't set a default XPS
configuration.  So you should probably setup XPS and you might also want
to try and make use of RPS to try and steer receive packets since the Rx
queues won't match the Tx queues.

After setting up XPS to CPU 1:1 binding, it works most of the time.
Meaning, most of the traffic will go through the TXQ I've bound the
process to, BUT some packets can still choose another TXQ (observed
monitoring tc output and blqmon).

Could this be related to the missing RPS setup?

Can I get some hints setting up RPS?

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Sr. Network Kernel Developer at Red Hat
  Author of http://www.iptv-analyzer.org
  LinkedIn: http://www.linkedin.com/in/brouer