On Thu, Oct 08, 2015 at 06:22:34PM +0100, Suzuki K. Poulose wrote: > On 08/10/15 15:45, Christoffer Dall wrote: > >On Wed, Oct 07, 2015 at 10:26:14AM +0100, Marc Zyngier wrote: > >>I just had a chat with Catalin, who did shed some light on this. > >>It all has to do with rounding up. What you would like to have here is: > >> > >>#define ARM64_HW_PGTABLE_LEVELS(va_bits) DIV_ROUND_UP(va_bits - PAGE_SHIFT, PAGE_SHIFT - 3) > >> > >>where (va_bits - PAGE_SHIFT) is the total number of bits we deal > >>with during a page table walk, and (PAGE_SHIFT - 3) is the number > >>of bits we deal with per level. > >> > >>The clue is in how DIV_ROUND_UP is written: > >> > >>#define DIV_ROUND_UP(n,d) (((n) + (d) - 1) / (d)) > >> > >>which gives you Suzuki's magic formula. > >> > >>I'd vote for the DIV_ROUND_UP(), which will make things a lot more readable. > >> > >Thanks for the explanation, I vote for DIV_ROUND_UP too. > > Btw, DIV_ROUND_UP is defined in linux/kernel.h, including which in the required > headers breaks the build. I could add the definition of the same locally. Or just keep the original magic formula and add the DIV_ROUND_UP one in a comment. -- Catalin -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
