Running Windows Server 2003 SP2 VMs on XenServer 5.5 (both update 1 and 2). Each VM has 5 x vCPUs and 7.5GB RAM. Hardware is Dell R710 with 2 x X5560 CPU and 24GB DDR3-1333. Three NICs all connected at 1Gbps to the same VLAN, two bonded and used as the VM network, the third used for XenCenter/management.
Connect from a Windows PC, all seems fine. Connect from an HP t5xxx WinCE thin client though and performance is appalling, switching from (e.g.) full screen IE8 to full screen Outlook 2007 takes far too long (we’re talking double-digit seconds).
Then found this Citrix Forum thread. See the post by Marcos Silva. Set the TCPIP DisableTaskOffload reg value within the Windows VM and rebooted it – problem solved. As you can see Citrix are not being overly effective at sorting this out…
Strange that the PC handles the mangled data better, but perhaps it has better buffering/TOE/etc. than the Windows CE thin client does.