Bug#755739: VGA-mode newcons very slow
On 25/07/14 19:42, Ed Maste wrote:
> On 22 July 2014 17:12, Steven Chamberlain <steven@pyro.eu.org> wrote:
>> I've seen the exact same thing under plain Qemu: newcons in VGA mode
>> seems very slow (but not as serious as you describe in Hyper-V).
>
> Can you quantify "very slow?" I've been testing vt(4) in QEMU on my
> FreeBSD host (so no KVM involved), and it's acceptably performant on
> my 8-core i7-3770 desktop.
This seems related to "-enable-kvm", and apparently also Hyper-V.
I managed to try again today with a fresh snapshot of 10-STABLE, using
Debian's packaging, configuration and build system (clang-3.4). I first
booted it from GRUB 2.00 in Qemu on linux-amd64, with
`qemu-system-x86_64 -enable-kvm -m 256`. It used kern.vty=vt, with the
vga driver.
With hw.vga.textmode=1, it takes about a second for the first kernel
messages to fill the screen; the only apparent delay here would be the
kernel doing things between printing each line of output.
With hw.vga.textmode=0, the same takes about 6 seconds, with noticeable
delay between printing each character (like a really slow serial tty)
and even slower once the screen is filled and starts to scroll.
I tried without -enable-kvm, and although it takes much longer to
decompress the kernel and start booting, the console output is fast
(screen is filled after 2 seconds) and scrolls at a normal speed.
Regards,
--
Steven Chamberlain
steven@pyro.eu.org
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