netdev - Re: macvtap performance regression (bisected) between 3.13 and 3.14-rc1

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Sat, 01 Mar 2014 12:15:14 +0100
From:	Christian Borntraeger <borntraeger@...ibm.com>
To:	vyasevic@...hat.com
CC:	"David S. Miller" <davem@...emloft.net>,
	Jason Wang <jasowang@...hat.com>,
	"Michael S. Tsirkin" <mst@...hat.com>, netdev@...r.kernel.org,
	KVM list <kvm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: macvtap performance regression (bisected) between 3.13 and 3.14-rc1

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