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 > > Maybe you remember, we had a similar situation with commit 3e4f8b787370978733ca6cae452720a4f0c296b8 > (macvtap: Perform GSO on forwarding path), the setup is basically the same. > > > Christian > > -- > To unsubscribe from this list: send the line "unsubscribe netdev" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- 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
