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[Qemu-devel] TCP Segementation Offloading
From: |
Ingo Krabbe |
Subject: |
[Qemu-devel] TCP Segementation Offloading |
Date: |
Sun, 1 May 2016 14:31:57 +0200 |
Good Mayday Qemu Developers,
today I tried to find a reference to a networking problem, that seems to be of
quite general nature: TCP Segmentation Offloading (TSO) in virtual environments.
When I setup TAP network adapter for a virtual machine and put it into a host
bridge, the known best practice is to manually set "tso off gso off" with
ethtool, for the guest driver if I use a hardware emulation, such as e1000
and/or "tso off gso off" for the host driver and/or for the bridge adapter, if
I use the virtio driver, as otherwise you experience (sometimes?) performance
problems or even lost packages.
I haven't found a complete analysis of the background of these problems, but
there seem to be some effects on MTU based fragmentation and UDP checksums.
There is a tso related bug on launchpad, but the context of this bug is too
narrow, for the generality of the problem.
Also it seems that there is a problem in LXC contexts too (I found such a
reference, without detailed description in a Post about Xen setup).
My question now is: Is there a bug in the driver code and shouldn't this be
documented somewhere in wiki.qemu.org? Where there developments about this
topic in the past or is there any planned/ongoing work todo on the qemu drivers?
Most problem reports found relate to deprecated Centos6 qemu-kvm packages.
In our company we have similar or even worse problems with Centos7 hosts and
guest machines.
I'm going to analyze these problems next week anyway and I woud be happy to
share my observation with you. (Where can I register for the wiki, or whom
should I sent my reports about this topic?).
Regards,
Ingo Krabbe
- [Qemu-devel] TCP Segementation Offloading,
Ingo Krabbe <=