Re: [Qemu-devel] [PULL 4/5] vfio-pci: Add debug config options to disable MSI/X KVM support

[Alex Williamson <alex.williamson@redhat.com>]

On Fri, 2013-12-06 at 23:06 +0100, Paolo Bonzini wrote:
> Il 06/12/2013 21:48, Alex Williamson ha scritto:
> >  /* Extra debugging, trap acceleration paths for more logging */
> >  #define VFIO_ALLOW_MMAP 1
> >  #define VFIO_ALLOW_KVM_INTX 1
> > +#define VFIO_ALLOW_KVM_MSI 1
> > +#define VFIO_ALLOW_KVM_MSIX 1
> 
> Why not make these device properties instead?

Honestly, I don't think they're that useful to the average or even to
the advanced user.  Each of these disables an acceleration/bypass path
and gives more logging output when debug is enabled.  Otherwise we don't
get debugging to see when mmap'd BARs are accessed and we can't tell
when interrupts happen relative to other accesses.  For instance it was
pretty obvious to find the Nvidia MSI ACK when seeing a config space
write immediately following an MSI injection.  Without debugging
enabled, these just slow things down and I don't know of any cases where
a device behaves better with these features disabled.  Thanks,

Alex