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

[Michael S. Tsirkin]

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.

> 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.

-- 
MST