Re: [Qemu-devel] [PATCH] Add option to slow down qemu

[Wolfgang Mauerer <wolfgang.mauerer@siemens.com>]

On 11/01/13 20:58, Stefan Weil wrote:
> Am 11.01.2013 14:40, schrieb Wolfgang Mauerer:
>> > For slow targets and fast hosts, the emulation may be faster
>> > than the actual hardware, which can be undesirable for various
>> > reasons. Add a run-time option to slow down the emulation
>> > by sleeping in the CPU emulation.
>> >
>> > Signed-off-by: Wolfgang Mauerer<wolfgang.mauerer@siemens.com>
>> > ---
>> >   cpus.c                |   34 ++++++++++++++++++++++++++++++++++
>> >   include/qemu-common.h |    2 ++
>> >   qemu-options.hx       |   13 +++++++++++++
>> >   vl.c                  |   10 ++++++++++
>> >   4 files changed, 59 insertions(+), 0 deletions(-)
>> >
>> > diff --git a/cpus.c b/cpus.c
>> > index 4a7782a..41a9e0c 100644
>> > --- a/cpus.c
>> > +++ b/cpus.c
>> > @@ -106,6 +106,11 @@ static QEMUTimer *icount_warp_timer;
>> >   static int64_t vm_clock_warp_start;
>> >   static int64_t qemu_icount;
>> >
>> > +static double slowdown_factor = 0.0;
>> > +#ifndef _WIN32
>> > +static struct timespec slowdown_delay;
>> > +#endif
>> > +
>> >    
> Hi,
> 
> slowdown_delay is used in configure_slowdown unconditionally,
> so I don't expect that the _WIN32 case will compile.
> 
> What about using g_usleep? It avoids the conditional compilation.
> 
> Is the comparison of double value "slowdown_factor" with 0.0
> time critical, or do all QEMU platforms have a fast FPU?
> 
> Setting a boolean value once and testing that value would
> be much faster of course.

I'm not sure if the floating point comparison has a significant
impact on any important platform, but using a boolean variable
makes the code more similar to the icount mechanism, so I've
changed it accordingly. Using g_usleep is a good idea to let the
conditional _WIN32 parts go away. Revised patch follows.

Cheers, Wolfgang