[Qemu-devel] Re: Precise guest instruction count.

[Steffen Liebergeld <usenet@gmx.eu>]

Hi,

Laurent Desnogues <laurent.desnogues@gmail.com> schrieb:
> On Wed, Mar 11, 2009 at 11:33 AM, Steffen Liebergeld <usenet@gmx.eu> wrote:
>> I temporarily disabled timers in Qemu, so normally time should not
>> influence my measurements.
>
> As Paul explained, in system mode there are other things that
> can cause interrupts, which you can't disable (unless you have
> your own emulated OS).

I am interested in which interrupts might occur, and how they influence the
instruction count. I am not using any input, and all output is sent to the
serial port via "-serial stdout".

I have a small assembler loop like the following pseudo code:
NOP
mov R1, $1000
loop:
    subs R1, $1
    bne loop
NOP

On every NOP Qemu prints the instruction count.

By turning of all timers in Qemu I hope to disable all timer interrupts for
the guest. The results I get are not correct for the first time the code is
run, but for all subsequent runs. In the first run, the instruction count has
12 additional instructions, which are not actually executed.

What is the cause of those additional instructions?

Greetings, Steffen