Re: [RFC PATCH 1/7] swiotlb: Instead of tracking the end of the swiotlb region just calculate it

[Alexander Duyck <alexander.h.duyck@intel.com>]

On 10/04/2012 06:01 AM, Konrad Rzeszutek Wilk wrote:
> On Wed, Oct 03, 2012 at 05:38:47PM -0700, Alexander Duyck wrote:
>> In the case of swiotlb we already have the start of the region and the number
>> of slabs that give us the region size.  Instead of having to call
>> virt_to_phys on two pointers we can just take advantage of the fact that the
>> region is linear and just compute the end based on the start plus the size.
> Why not take advantage of 'the fact that the region is linear' and just
> pre-compute the end in swiotlb_init_with_tbl?
>
> That way the logic in is_swiotlb_buffer is even simpler?
>

Using a pre-computed end point based on a virtual address is more
expensive in the x86_64 case.  The calls to __phys_addr require a
separate function call.  By just using the physical address of the start
and adding the offset I can avoid the second call and the compiler will
take advantage of the smaller function size.  The result is that
is_swiotlb_buffer will be inlined.

Thanks,

Alex