On 03/03/2014 04:13 AM, Christian Borntraeger wrote: > 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. Hi Christian Just sent out a patch to fix this. I tried it with namespaces and kvm guests and it seems to restore performance for me. Please give it a try. Thanks -vlad > > 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
