On Sun, May 01, 2016 at 02:31:57PM +0200, Ingo Krabbe wrote: > 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 can't parse this sentence. In what cases do you think it's a "known best practice" to disable tso and gso? Maybe a table would be a clearer way to communicate this. Can you provide a link to the source claiming tso and gso should be disabled? > 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. Have haven't explained what problem you are experiencing. If you want help with your setup please include your QEMU command-line (ps aux | grep qemu), the traffic pattern (ideally how to reproduce it with a benchmarking tool), and what observation you are making (e.g. netstat counters showing dropped packets). > 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?). I have CCed Michael Tsirkin and Jason Wang. They do most of the virtio-net development. > > Regards, > > Ingo Krabbe > >
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