|Subject:||Re: [Qemu-devel] [PATCH] intentinoal slowing down qemu - brake|
|Date:||Wed, 6 Dec 2006 12:33:47 +0530|
I'm sending some more facts that should make clear why I think the
functionality provided by the patch is relevant. (At least for the DOS
Making emulated CPU slower
Some old DOS games runs too fast on modern CPUs, even the qemu-emulted
ones. This patch can make these games playable.
The problem was reported in http://qemu-forum.ipi.fi/viewtopic.php?t=1264
MSDOS doesn't use HLT insn. Even if the dosidle can help in command
prompt, it doesn't work in other programs such as games.
This was reported in http://qemu-forum.ipi.fi/viewtopic.php?t=1372
The similar approach is used in dosbox by setting "CPU cycles". I think
qemu is better than dosbox, so it makes sense to me to include such
This patch doesn't try to emulate the task scheduler that was why Martin
voted against it. I'm sorry if I wasnt't clear enough in my first post.
On Thu, 30 Nov 2006, Miroslav Novak wrote:
> This patch adds support for slowing down qemu and saving cpu load.
> The '-brake' command line parameter or monitor command 'brake' determines how
> long to wait in the main_loop with respect to duration of time that qemu used
> for the emulation itself.
> Thus e.g. zero value runs at full speed, 1 at 1/2 speed, 10 at 1/11 speed,
> A drawback of this approach is that the timer interrupt can be missed if
> raised too often. This happens if the loop_main divided by (1+brake) is less
> than the frequency of PIC interrupts.
> In such case the time of emulated system runs slowly.
> This problem occurs mainly for Linux emulation where kernel parameter HZ is of
> several hunderds.
> For DOS emulation, where the timer interrupts are raised usualy at 18Hz, this
> approach works nice, and one can play old DOS games at reasonable speed and
> save batteries.
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