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

[Paolo Bonzini]

Il 06/12/2013 23:36, Alex Williamson ha scritto:
>>> > >  #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.

Yeah, behaving better is unlikely.  I was thinking of them as a
debugging features.

As to debug messages, have you considered replacing them with tracepoints?

Paolo