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SubjectRe: macvtap performance regression (bisected) between 3.13 and 3.14-rc1
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.

-vlad

>
>
> Christian
>



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