On 02/03/14 02:21, Vlad Yasevich wrote: > On 03/01/2014 02:27 PM, Vlad Yasevich wrote: >> On 03/01/2014 06:15 AM, Christian Borntraeger wrote: >>> On 28/02/14 23:14, Vlad Yasevich wrote: >>>> On 02/27/2014 03:52 PM, Christian Borntraeger wrote: >>>>> Vlad, >>>>> >>>>> commit 6acf54f1cf0a6747bac9fea26f34cfc5a9029523 >>>>> macvtap: Add support of packet capture on macvtap device. >>>>> >>>>> causes a performance regression for iperf traffic between two KVM guests >>>>> on my s390 system. Both guests are connected via two macvtaps on the same OSA >>>>> network card. >>>>> Before that patch I get ~20 Gbit/sec between two guests, afterwards I get >>>>> ~4Gbit/sec >>>>> >>>>> Latency seems to be unchanges (uperf 1byte ping pong). >>>>> >>>>> According to ifconfig in the guest, I have ~ 1500 bytes per packet with this >>>>> patch and ~ 40000 bytes without. So for some reason this patch causes the >>>>> network stack to do segmentation. (the guest kernel stays the same, only host >>>>> kernel is changed). >>>>> >>>>> Any ideas? >>>> >>>> I am looking. It shouldn't cause addition segmentations and when I ran >>>> netperf on the code I didn't see any difference in the throughput. >>> >>> Dont know if the different bytes/packets ratio is really the reason or >>> just a side effect. As a hint: the underlying network device does not support >>> segmentation, but this should not matter for traffic between to guests. >> >> Could you post 'ethtool -k' output for both lower-level device and the >> macvtap device? >> >> Thanks >> -vlad >> > > Ok. I think I see what's happening. Since you turn off offloads on > lower device, that's propagated to macvlan device. As a result, when > when we call dev_queue_xmit on the vlan->dev, we end up segmenting since > lower level says it does support segmentation. > > One way to fix this is to never disable offloads on macvlan. macvlan > will always try to use __dev_queue_xmit() with it's lower device, so any > segmentation can happen there. If you have anything that I should test, let me know. Christian -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
