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. 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 kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
