[syslinux] Syslinux 4.04 gpxelinux.0 http performance problem with VMware VMs
Pasi Kärkkäinen
pasik at iki.fi
Mon May 7 13:40:48 PDT 2012
Hello,
In my testing environment I have two VMs on ESXi 5.0.
VM A = dhcp/tftp/PXE/http server, running CentOS 6.2. Syslinux 4.04 with the included gpxelinux.0.
VM B = PXE boot client.
If I run CentOS 6.2 also on the VM B, I can easily transfer 50+ MB/sec over http between the VMs (wget, links).
Now, if I PXE boot gpxelinux.0 on the VM B, and start to download bigger initrd image
over http the download speed is very slow: only 200 - 500 kB/sec.
I tried using both Intel e1000 and vmxnet3 NICs on the VM B.
No big difference, both were slow.
I tried moving the VMs on the same host, and also to separate hosts - no difference.
Then I noticed there's a lot of TCP retransmit happening when gpxelinux.0 client
downloads files from the http server.. dozens or even hundreds of retransmit per second.
Any ideas what could cause that?
Then I noticed if I use ethtool to disable all offloads (lro/gro/rx/tx) on the VM A NIC
the download speed jumps to 1700 - 2800 kB/sec. So that's WAY better speed.
But still there's a lot tcp retransmits happening all the time..
Any ideas what's causing the bad performance and those continuous retransmits?
Anything I should try to debug this?
On baremetal with Intel NICs I've seen much better gpxelinux.0 download speeds over http.
Thanks,
-- Pasi
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