On Thu, Oct 15, 2015 at 02:48:47PM +0100, Suzuki K. Poulose wrote: > On 15/10/15 14:30, Christoffer Dall wrote: > >On Thu, Oct 15, 2015 at 02:14:22PM +0100, Suzuki K. Poulose wrote: > >>On 15/10/15 13:44, Mark Rutland wrote: > >>>On Thu, Oct 15, 2015 at 01:37:35PM +0200, Christoffer Dall wrote: > >>>>On Wed, Oct 14, 2015 at 12:20:26PM +0100, Suzuki K. Poulose wrote: > > > >> * The maximum number of levels supported by the architecture is 4. Hence > >> at starting > >> * at level n, we hanve (4 - n) levels of translation. So, the total > >> number of bits > > > >nit: s/hanve/have/ > > Fixed. > > > > >> * mapped by an entry at level n is : > >> * > >> * ((4 - n) - 1) * (PAGE_SHIFT - 3) + PAGE_SHIFT > >> * > >> * Rearranging it a bit we get : > >> * (4 - n) * (PAGE_SHIFT - 3) + 3 > >> */ > >> > >>Or we could use the formula without rearranging. > >> > >Either way, even I get it now. > > > >Thanks for the explanation!! > > :). I was involved too much in these calculations that, the formula looked > obvious to me, when I wrote it. But yes, I did realise that it is indeed > complicated, once I really started looking at explaining why I wrote it so. > Thanks for being patient :) and complaining peacefully ! > > Btw, I have a revised (hopefully better) version here : > > /* > * Size mapped by an entry at level n ( 0 <= n <= 3) > * We map (PAGE_SHIFT - 3) at all translation levels and PAGE_SHIFT bits > * in the final page. The maximum number of translation levels supported by > * the architecture is 4. Hence, starting at at level n, we have further > * ((4 - n) - 1) levels of translation excluding the offset within the page. > * So, the total number of bits mapped by an entry at level n is : > * > * ((4 - n) - 1) * (PAGE_SHIFT - 3) + PAGE_SHIFT > * > * Rearranging it a bit we get : > * (4 - n) * (PAGE_SHIFT - 3) + 3 > */ >
Looks good. > > > > >Assuming some version of this goes in: > > > >Acked-by: Christoffer Dall <christoffer.d...@linaro.org> > > > > Thanks. I lost two interview questions though ;) > There are plenty of good sources for that in the KVM/ARM code. -Christoffer -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
