Re: [Qemu-devel] Timing problems

From: Oliver Gerlich <olig9@gmx.de>
To: Alexander Toresson <alexander.toresson@gmail.com>, qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] Timing problems
Date: Wed, 29 Jun 2005 15:21:06 +0200	[thread overview]
Message-ID: <42C2A042.4050304@gmx.de> (raw)
In-Reply-To: <b33ba6660506290108431d0540@mail.gmail.com>

Alexander Toresson wrote:
> I'm running windows 2000 in qemu 0.7.0 with kqemu 0.6.2-1 on i386
> debian linux. First thing I tried to do was to run a benchmark program
> (qemu w/o kqemu vs qemu w/ kqemu). I got strange results, and I also
> noted that timing didn't seem to be that good, so I re-tried to run
> the benchmark program, but with the date & clock settings window in
> the background. This is the result: The more cpu that is used in the
> virtual cpu, the faster time flies by. For example, when it's nearly
> idle, time is too slow. If it goes from idle to 100% cpu-use, time
> flies by at 5x the speed it should. This is true both when I use kqemu
> and when I don't. This cpu is capable of speedstep, but I have
> disabled it while doing this test. I think I would get even more weird
> results if I enabled it.
> This makes it impossible to run a benchmark and get any useful results
> out of it. Also, trying to run a game on qemu would be a disaster.

Not necessarily, Age of Empires 2 runs quite well under Qemu + Win98SE 
(on an Athlon 2600+, host: Debian Linux, kernel 2.6.9).

> However, running normal programs aren't any problem. Except that I
> have to be very quick when changing resolution in w2k (it should wait
> 15s, now time flies away and those 15 becomes 2s :)).
> 
> Before compiling qemu 0.7.0 with kqemu 0.6.2-1, I ran qemu
> 0.6.something, taken from the debian testing repository, and it had
> the same problem.
> 
> Regards, Alexander Toresson
> 
> PS. I'm susprised nobody has seen this problem before. Is it just me
> who experience it?

Although I use Visual Studio 5 and Age of Empires 2 inside Qemu (with 
Win98SE and Win2k), I never noticed such problems, and the Windows clock 
always seemed quite right (and VC++ stresses the CPU quite a lot!). But 
admittedly I never ran benchmarks or had a closer look at the guest 
system time.

Regards,
Oliver Gerlich

> 
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