[syslinux] "Tick-counting" vs "Tick-less" timekeeping issues on VMs emulating BIOS PCs

[Patrick Masotta]

Before 6.X Syslinux used a "Tick-less" timekeeping approach implemented in 

/core/bios.inc 

6.X now implements a "Tick-counting" strategy (timer interrupt) implemented in 

/core/timer.inc

I think this change presents issues when Sysylinux runs on Virtual Machines 

emulating a BIOS environment as they cannot correctly emulate the timer interrupt; 

see VMware's pdf:

https://www.vmware.com/files/pdf/Timekeeping-In-VirtualMachines.pdf

At the moment I'm seeing timing issues on TFTP transfers (lwIP depends
on the new interrupt based timer). I have consistently detected 

multiple Requests, double ACKs, etc. All these problems seem to be

sourced on the now unreliable timeouts.
I have used TFTP on the same (BIOS VM) scenarios with 3.X and TFTP 

timing was always rock solid.


Sorry if this was discussed before, if not I'd like to ask (Peter) if 

there is any reason preventing us from going back to the "Tick-less" 

approach. Thanks.


Best
Patrick