[syslinux] Syslinux 4.04 gpxelinux.0 http performance problem with VMware VMs

[Pasi Kärkkäinen]

On Tue, May 08, 2012 at 09:32:26PM +0300, Pasi Kärkkäinen wrote:
> On Tue, May 08, 2012 at 08:44:01PM +0300, Pasi Kärkkäinen wrote:
> > > > 
> > > > Hello Pasi,
> > > > 
> > > > As I understand it, simply chain pxelinux.0 (from the 4.10-pre* line)
> > > > to your PXE client as the boot file, and it'll speak HTTP if it's
> > > > given an HTTP URI from the pxelinux.cfg/default (or client specific
> > > > named) config file.
> > > > 
> > > 
> > > Thanks for confirming that!
> > > 
> > > > I'd suspect that if you want to pull HTTP for the config file as well,
> > > > you'd have to set your DHCP options accordingly, notably the pxelinux
> > > > Path Prefix, or DHCP option 210, along with the "pxelinux magic"
> > > > options.  Detailed here:
> > > > http://www.syslinux.org/wiki/index.php/PXELINUX#Can_I_send_information_to_PXELINUX_via_special_options_in_the_DHCP_response.3F
> > > > 
> > > 
> > > Yeah I've been pulling also the config file over HTTP with gpxelinux.0,
> > > so I assume I need pretty much the same DHCP config/options when using 
> > > the new pxelinux.0 from 4.10-pre*. 
> > > 
> > > > Been meaning to try it out myself since I downloaded the binaries a
> > > > few days ago :)
> > > > 
> > > 
> > > Good luck :) I'll try it today/tomorrow aswell.
> > > 
> > 
> > I just tried with pxelinux.0 from syslinux-4.10-pre20.
> > 
> > Now I can get up to 6 MB/sec http download speed when using 
> > vmxnet3 NIC in the PXE boot VM. 
> > 
> > If I use e1000 NIC in the PXE boot VM the speed is slower, 
> > around 1.0 - 1.5 MB/sec.
> > 
> > So now it's better but still not quite there..
> > 
> > I can still see a lot of TCP retransmits on the http server (CentOS 6.2) side.
> > While downloading 260 MB image over http I can see around 5900 TCP retransmits 
> > happening on the http server! That doesn't sound right.. 
> > 
> > Can someone think of Linux network settings that might affect this on the http server side? 
> > 
> 
> Actually it's all these counters from "netstat -s" that increase at (about) the same rate:
> 
> 6583 segments retransmited
> 6243 times recovered from packet loss due to fast retransmit
> 6326 fast retransmits
> 
> Does that ring any bells to anyone? 
> There are no errors or drops on the eth0 nic level (in ifconfig output).
> 

And one more mail to my monologue.. 

After the PXE boot in the VM is complete and I transfer the *same* file over http
from *Linux*, I don't get (almost) any TCP retransmits! 

So the big amount of TCP retransmits is only happening when pxelinux.0 is downloading over http..

-- Pasi