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
eth1->xenbr1
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?
-- 
--tmac
RedHat Certified Engineer #804006984323821 (RHEL4)
RedHat Certified Engineer #805007643429572 (RHEL5)
Principal Consultant, RABA Technologies
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