Re: [PATCH 02/11] iommu-api: Add iommu_map and iommu_unmap functions

[Avi Kivity]

On 02/07/2010 12:50 PM, Joerg Roedel wrote:
> On Sun, Feb 07, 2010 at 11:38:30AM +0200, Avi Kivity wrote:
>    
> > On 01/28/2010 01:37 PM, Joerg Roedel wrote:
> >      
> > > These two functions provide support for mapping and
> > > unmapping physical addresses to io virtual addresses. The
> > > difference to the iommu_(un)map_range() is that the new
> > > functions take a gfp_order parameter instead of a size. This
> > > allows the IOMMU backend implementations to detect easier if
> > > a given range can be mapped by larger page sizes.
> > > These new functions should replace the old ones in the long
> > > term.
> > >
> > >        
> > These seem to be less flexible in the long term.  Sure, it is easier for
> > the backend to map to multiple page sizes if your iommu supports
> > arbitrary power-of-two page sizes, but we should make the APIs easier
> > for the callers, not the backend.
> >      
> These functions are as flexible as the old ones which just tok a size.
> The benefit of the new interface is that is makes the ability of the
> IOMMU to map the area with a large page (an get the benefit of fewer
> hardware tlb walks) visible to the caller. With the old interface the
> caller is tempted to just map ist whole area using 4kb page sizes.
> It gives a bit more complexity to the caller, thats right. But given
> that the page allocator in Linux always returns pages which are aligned
> to its size takes a lot of that complexity away.
>
>    

You are right - I was thinking of the kvm use case which is range 
oriented, but the ordinary kernel interfaces are gfp_order oriented.

--
error compiling committee.c: too many arguments to function

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