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Re: [Xen-users] Xen and networking.

To: tmac <tmacmd@xxxxxxxxx>
Subject: Re: [Xen-users] Xen and networking.
From: Riccardo Veraldi <Riccardo.Veraldi@xxxxxxxxxxxx>
Date: Sun, 30 Dec 2007 13:11:13 +0100
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if you want to get Gigabit performance on your domU (using HVM virtualization) you MUST compile the xen unmodified_drivers (in particular Netfront) and load
those drivers as kernel modules on your domU.
Then you must change the guest machine xen file using netfront insted of ioemu for the network interface. I have written a page on how to do it but it is written in italian. Anyway if you follow the instruction you should understand looking at the bare commands.


of couse the xen source coude depends on the xen version you are using on your dom0. Actually I was not satisfied of Xen 3.0.2 used on RHEL5 so we build rpm for Xen 3.1.2
and actually we are using those.


tmac ha scritto:
I have a beefy machine
(Intel dual-quad core, 16GB memory 2 x GigE)

I have loaded RHEL5.1-xen on the hardware and have created two logical systems:
4 cpus, 7.5 GB memory 1 x Gige

Following RHEL guidelines, I have it set up so that eth0->xenbr0 and
Each of the two RHEL5.1 guests uses one of the interfaces and this is
verified at the
switch by seeing the unique MAC addresses.

If I do a crude test from one guest over nfs,
dd if=/dev/zero of=/nfs/test bs=32768 count=32768

This yields almost always 95-100MB/sec

When I run two simultaneously, I cannot seem to get above 25MB/sec from each.
It starts off with a large burst like each can do 100MB/sec, but then
in a couple
of seconds, tapers off to the 15-40MB/sec until the dd finishes.

Things I have tried (installed on the host and the guests)

 net.core.rmem_max = 16777216
 net.core.wmem_max = 16777216
 net.ipv4.tcp_rmem = 4096 87380 16777216
 net.ipv4.tcp_wmem = 4096 65536 16777216

 net.ipv4.tcp_no_metrics_save = 1
 net.ipv4.tcp_moderate_rcvbuf = 1
 # recommended to increase this for 1000 BT or higher
 net.core.netdev_max_backlog = 2500
 sysctl -w net.ipv4.tcp_congestion_control=cubic

Any ideas?

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