Re: [9fans] I/O load crashes Qemu

[erik quanstrom <quanstro@quanstro.net>]

> On a T42 running FreeBSD,  a stock FreeBSD-4.11/qemu gets
> 18MB/s & plan9/qemu gets 3MB/s.  Both tested by writing 100MB
> from /dev/zero to a file.  Neither needs any special drivers.
>
> I think part of the performance problem is qemu emulates an
> early Intel ATA controller chip (PIIX3) and perhaps plan9
> does not do certain optimizations.  It would not be too hard
> to emulate a more modern controller.

try turning dma on.  it is very unlikely that plan 9 is missing some
important ata optimization.

> IMHO a virtualizable processor is the necessary first step as
> it clears one's mind about what not to do in an efficient
> virtualizable IO architecture!

unless you are contemplating a processor with i/o instructions,
what does the processor have to do with i/o architecture?

> Emulating grotty device
> registers with horrible side-effects is just too painful and
> one would be forced to abstract that out.  Probably too late
> for that!

i find there's a certain simplicty in dealing directly
with hardware, provided one has documentation.

but just wait, there will come a day when people complain
about the nasty registers in vm and how it would be good to
abstract that stuff out.

i think that may have been yesterday.

- erik