Re: [Qemu-devel] [PATCH 03/13] iommu: Add universal DMA helper functions

[Anthony Liguori]

On 06/20/2012 04:42 PM, Michael S. Tsirkin wrote:
> On Wed, Jun 20, 2012 at 04:38:30PM -0500, Anthony Liguori wrote:
> > On 06/20/2012 04:32 PM, Michael S. Tsirkin wrote:
> > > On Wed, Jun 20, 2012 at 04:16:47PM -0500, Anthony Liguori wrote:
> > > > > diff --git a/hw/pci.h b/hw/pci.h
> > > > > index 7f223c0..ee669d9 100644
> > > > > --- a/hw/pci.h
> > > > > +++ b/hw/pci.h
> > > > > @@ -558,10 +558,16 @@ static inline uint32_t pci_config_size(const PCIDevice *d)
> > > > >   }
> > > > >
> > > > >   /* DMA access functions */
> > > > > +static inline DMAContext *pci_dma_context(PCIDevice *dev)
> > > > > +{
> > > > > +    /* Stub for when we have no PCI iommu support */
> > > > > +    return NULL;
> > > > > +}
> > > >
> > > > Why is all of this stuff static inline?
> > >
> > > Let's face it, most people don't need an MMU in their VM.
> > > inline stubs help make double sure we are not adding
> > > overhead for the sake of this niche case.
> >
> > It also makes for an overly complex pci.h with no obvious performance 
> > justification.
> A stub in a header plus an offline empty function is even more useless
> code. inline stubs is standard procedure.

Look at 8/13.  They don't stay stubs for long.

Regards,

Anthony Liguori

> > Let's not prematurely optimize here.
> >
> > Regards,
> >
> > Anthony Liguori
>
> It's not just an optimization.  It is easier to see what's going on this
> way.