On Thu, Oct 04, 2012 at 08:54:09AM -0700, Alexander Duyck wrote: > 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. Right, that is not what I was thinking. My thought was that since you are already computing the start of the DMA address, you can also compute the end - and save both values in a global variable. Then use said global variables to check for your DMA instead of doing the extra compution of shifting to find the end of the DMA address. > > Thanks, > > Alex _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/devel
