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xen-users
Re: [Xen-users] Release 0.8.0 of GPL PV Drivers for Windows
On Sunday 02 March 2008 04:51:47 am Pasi Kärkkäinen wrote:
> Yep. I asked because of the "bad" 80 Mbit/sec result on a 100 Mbit network..
My guess is my cpu(s) don't have enough raw power to saturate the nic, but
let's see what happens after your suggestions are implemented.
> That's because with some version of xen and/or drivers (I'm not sure
> actually) it was a known fact that performance got bad when you had hw
> checksum calculations turned on..
>
> So just to see if that's the case here.. I guess this was mostly for domU..
Ahh, because there's no hardware - makes sense.
Alright - let's try one change/set of related changes at a time to isolate
their effect.
> > rx-checksumming: off
> > tx-checksumming: off
> > scatter-gather: off
> > tcp segmentation offload: off
> > udp fragmentation offload: off
> > generic segmentation offload: off
>
> Maybe try turning on offloading/checksumming settings here?
Ok - before any changes, 'iperf -c insp6400 -t 60' gives 78.7 Mbps.
On SuSE:
[830] > sudo ethtool -K eth0 tx on
Cannot set device tx csum settings: Operation not supported
[2] 23551 exit 85 sudo ethtool -K eth0 tx on
jimb@Dell4550 03/02/08 10:36AM:~
[831] > sudo ethtool -K eth0 tso on
Cannot set device tcp segmentation offload settings: Operation not supported
[2] 23552 exit 88 sudo ethtool -K eth0 tso on
on fc8:
[742] > sudo ethtool -K peth0 tx on
Password:
Cannot set device tx csum settings: Operation not supported
zsh: exit 85 sudo ethtool -K peth0 tx on
jimb@Insp6400 03/02/08 10:38AM:~
[743] > sudo ethtool -K peth0 tso on
Cannot set device tcp segmentation offload settings: Operation not supported
zsh: exit 88 sudo ethtool -K peth0 tso on
Ahem - moving on!
> I usually use at least 256k window sizes :)
Trying adding '-w 262144' on both server and client side, iperf gets 72.1
Mpbs. Worse.
> Did you try with multiple threads at the same time? Did it have any effect?
Adding '-P 4' to client, iperf gets an aggregate rate of 74.5 Mpbs. Worse.
> "ifconfig eth0 txqueuelen <value>" on linux.. I don't know how to do that
> in windows.
>
> But it's important to do that on dom0 for vifX.Y devices.. those are the
> dom0 sides of the virtual machine virtual NICs.
[740] > ifconfig
[...]
peth0 Link encap:Ethernet HWaddr 00:15:C5:04:7D:4F
inet6 addr: fe80::215:c5ff:fe04:7d4f/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1492 Metric:1
RX packets:11545320 errors:0 dropped:237 overruns:0 frame:0
TX packets:13476839 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:421343991 (401.8 MiB) TX bytes:4224204231 (3.9 GiB)
Interrupt:22
tap0 Link encap:Ethernet HWaddr 0E:92:BB:CA:D8:DA
inet6 addr: fe80::c92:bbff:feca:d8da/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:14090 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:500
RX bytes:0 (0.0 b) TX bytes:7860525 (7.4 MiB)
vif4.0 Link encap:Ethernet HWaddr FE:FF:FF:FF:FF:FF
inet6 addr: fe80::fcff:ffff:feff:ffff/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:2595441 errors:0 dropped:0 overruns:0 frame:0
TX packets:923150 errors:0 dropped:795 overruns:0 carrier:0
collisions:0 txqueuelen:32
RX bytes:3366016758 (3.1 GiB) TX bytes:166299319 (158.5 MiB)
vif16.0 Link encap:Ethernet HWaddr FE:FF:FF:FF:FF:FF
inet6 addr: fe80::fcff:ffff:feff:ffff/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:9848 errors:0 dropped:0 overruns:0 frame:0
TX packets:20828 errors:0 dropped:4698 overruns:0 carrier:0
collisions:0 txqueuelen:32
RX bytes:834219 (814.6 KiB) TX bytes:16017488 (15.2 MiB)
Yowza! 32? Those *are* small!
500 isn't much better for tap0, either.
> > > - Check sysctl net.core.netdev_max_backlog setting.. it should be at
> > > least 1000, possibly even more.. this applies to dom0 and linux domU.
> >
> > Where is this set, and what do I have to restart to make it
> > effective? /etc/sysctl.conf?
>
> Yep, modify /etc/sysctl.conf and run "sysctl -p /etc/sysctl.conf".
>
> > In general, are there any downsides in changing these values?
>
> http://kb.pert.geant2.net/PERTKB/InterfaceQueueLength
Interesting link - thanx.
Ok - setting 'ifconfig eth0 txqueuelen 2500' (peth0 on fc8) and
net.core.netdev_max_backlog = 2500 on both machines, iperf gets 65.9 Mpbs.
Worse. Probably only useful for Gpbs links. Removing changes, as in all cases
above.
> There's something about these settings
>
> btw. what was the CPU usage for dom0 and for domU when you did these iperf
> tests?
About 75%. I've noticed, at least on my SuSE box, that multimedia playback
suffers over 50%. (wine)
On my WIndows guest, setting tap0's txqueuelen to 1000 had no effect (it
probably wouldn't since it's receiving); setting window size to 256k hung my
guest; after rebooting the guest, it had no effect on 2nd try; and changing
sysctl had no effect. Cpu % was about 80-85% w/o any changes (negligible on
fc8) averaged over 2 vcpus. With any of the changes above, cpu % went down to
65-75% - the only change noticed.
Have fun digesting this :-)
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