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

On 02/03/16 22:47, Patrick Masotta via Syslinux wrote:
> Not really, a virtual environment can easily emulate the BIOS_timer	at
0x046C
> but it has problems emulating a "real" timer interrupt to be
hooked...
> That's the real problem.
The timer interrupt works fine in at least KVM, Xen, VMware, and 
Hyper-V.  (I've tested iPXE in all of those virtual environments, and 
iPXE relies on the timer interrupt actually triggering a call to an ISR 
within the VM.)

Michael

On March 2, 2016 3:45:14 PM PST, Michael Brown <mcb30 at ipxe.org>
wrote:
>On 02/03/16 22:47, Patrick Masotta via Syslinux wrote:
>> Not really, a virtual environment can easily emulate the
>BIOS_timer	at 0x046C
>> but it has problems emulating a "real" timer interrupt to be
>hooked...
>> That's the real problem.
>
>The timer interrupt works fine in at least KVM, Xen, VMware, and 
>Hyper-V.  (I've tested iPXE in all of those virtual environments, and 
>iPXE relies on the timer interrupt actually triggering a call to an ISR
>
>within the VM.)
>
>Michael
And the document you link to states so.
-- 
Sent from my Android device with K-9 Mail. Please excuse brevity and formatting.

>>>
> Not really, a virtual environment can easily emulate the BIOS_timer    at
0x046C
> but it has problems emulating a "real" timer interrupt to be
hooked...
> That's the real problem.
The timer interrupt works fine in at least KVM, Xen, VMware, and 
Hyper-V.  (I've tested iPXE in all of those virtual environments, and 
iPXE relies on the timer interrupt actually triggering a call to an ISR 
within the VM.)


Michael
<<<


Well, that contradicts what the VMware document says.
I'm still working on this; probably there are other hidden timing 

issues affecting TFTP when it's run on a VM. I'll post what I find.

Best,
Patrick

On 03/03/16 07:31, Patrick Masotta wrote:
> > The timer interrupt works fine in at least KVM, Xen, VMware, and
> > Hyper-V.  (I've tested iPXE in all of those virtual environments,
and
> > iPXE relies on the timer interrupt actually triggering a call to an
ISR
> > within the VM.)
>
> Well, that contradicts what the VMware document says.
How so?

Michael