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Re: [Qemu-devel] Timing problems

From: Oliver Gerlich
Subject: Re: [Qemu-devel] Timing problems
Date: Wed, 29 Jun 2005 15:21:06 +0200
User-agent: Mozilla Thunderbird 1.0.2-1 (X11/20050519)

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.

Oliver Gerlich

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