Syslinux - Mar 2016 - "Tick-counting" vs "Tick-less" timekeeping issues on VMs emulating BIOS PCs

On 03/03/16 09:45, Patrick Masotta wrote:
> > At the BIOS standard rate of 18.2Hz, no modern machine is even going
to
> > notice.
>
> I think they do when running a VM,
>
> That's why my Debian VM date is always indicating whatever,
> no matter how many times I reset the time of the day.
> (Running on a i7-3630QM host)
> For some reason they cannot emulate a good timer interrupt.
Your Linux guest will have reconfigured the timer interrupt to run 
faster than the BIOS standard rate of 18.2Hz.

Michael

>>>
Your Linux guest will have reconfigured the timer interrupt to run 
faster than the BIOS standard rate of 18.2Hz.


Michael
<<<

It could be; I really do not know.

Bottom line; There are timing issues with TFTP transfers 

on VM machines emulating BIOS hardware. 

Probably the interrupt based timer is not the culprit; 

now I'm working on /core/fs/pxe/core.c trying to see if 

there's something wrong there.


Best,
Patrick

>>>
...
Bottom line; There are timing issues with TFTP transfers 
on VM machines emulating BIOS hardware. 
Probably the interrupt based timer is not the culprit; 
now I'm working on /core/fs/pxe/core.c trying to see if 
there's something wrong there.

Best,

Patrick
<<<

I've been working on this issue, I have tested the timers,
and as you guys mentioned before they are OK.
I've noticed that if the VMware VM uses the driver e1000e everything is
"OK"
but if the VM uses the "vmxnet3" the problem is there.
I have attached a small pcap file showing the end of the lpxelinux.0 TFTP
transfer and the

beginning of the problematic ldlinux.c32 transfer.
I wonder if the "vmxnet3" driver is probably "too fast" for
the Sequential lwIP API?


Best,
Patrick
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