[Qemu-devel] relative time

[Qemu-devel] relative time

[Markus Schiltknecht]

Hello qemu developers,

I've been unable to find information about date and time in qemu. Two 
questions the simpler one:

Can I set the date and time of the system clock at start of the 
emulation (or in the manager console)? I've seen a patch [1], but that 
doesn't seem to be included in my build (from debian sid):

Now the more complex one: I would like to do 'relative benchmarks', i.e. 
comparing one product to another. I don't mind very much how fast my 
machines are, but I want them to be equally fast, even if I use two, 
three or ten of those on my machine.

Therefore I would like to limit CPU time. Say limiting it to virtually 1 
MHz. Optionally one could even take into account processor caches...

As some of the benchmarks I would like to run are harddrive dependant, 
could one limit their speed? Try simulating harddisk head positions and 
rotation?

Limiting the network speed can be done quite accurately with Linux on 
tap devices I don't know about latency, though.

All in all: I would like to simulate a system which is exactly (or quite 
close to) a 100 times slower than a given real one.

Has anybody tried (or requested) something like that already? How 
difficult would it be to teach qemu to 'slow down'? How accurate could 
such a slow down be?

Regards

Markus

[1]: http://lists.gnu.org/archive/html/qemu-devel/2006-01/msg00128.html

Re: [Qemu-devel] relative time

[Paul Brook]

> Now the more complex one: I would like to do 'relative benchmarks', i.e.
> comparing one product to another. I don't mind very much how fast my
> machines are, but I want them to be equally fast, even if I use two,
> three or ten of those on my machine.

qemu is not, and does not try to be cycle accurate. Any benchamrks you do on 
qemu bear no relationship whatsoever to how things will perform on real 
hardware.

Paul