VGA Console interference

TUD-OS / NRE

NOVA runtime environment (official branch)

GNU General Public License v2.0

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VGA Console interference #30

Closed parthy closed 11 years ago

parthy commented 11 years ago

Sometimes the NOVA console output (spinner) flashes in a guest console. Steps to reproduce for me:

./b srvp boot/vmmng
Boot Linux
Log in
Type dmesg: Can already see characters flashing in the bottom line
Scroll up via Shift + PGUP until further flashing characters appear.

It seems that if the guest uses more VGA pages, this problem occurs. Can anyone else confirm this?

Nils-TUD commented 11 years ago

Yes, this is known. The reason is that the clients of the console service get direct access to the VGA memory. Thus, if NOVA writes to these pages as well, it interferes. The only way I can think of to prevent that would be to not give them direct access but copy the content of the current VGA page to a different one than NOVA. But that would be a waste of time, IMO. Although, I have to admit that we currently do a copy in NRE's seoul backend anyway, but this is only done for simplicity and for preventing changes in seoul. So, as a workaround, just disable the spinner :)

udosteinberg commented 11 years ago

For performance reasons it's good that NRE writes directly to the VGA framebuffer, so I wouldn't want to see that changed. So as Nils said, just disable spinners or use the novga parameter on the hypervisor command line.

parthy commented 11 years ago

Okay, that sounds reasonable. Thanks for the explanation :)