Dan Malek <dan at embeddededge.com> wrote: > > On Jul 26, 2004, at 2:33 PM, Linh Dang wrote: > >> My understanding is: >> >> - mmap(2) uses pages to map the device (my platform doesn't have large >> page.) > > Yes, so? > >> - mapping a large address range (hundreds-of-megabytes) is much more >> efficient with BATs than with pages. > > Depends upon your measurement of efficiency. > >> So, do you mean: >> - mmap(2) can use BATs? or > > Not likely due to alignment and size constraints. > >> - the difference in performance is negligible between BATs and >> pages when mapping an address range of 200MBs? > > If you can measure or are affected by the difference, there are many > more things that will ensure your software will not work properly.
What do you mean by the above sentence? - 200MB would need 51200 ptes. that means doubling the current number of ptes on my system. - If using block mapping doesn't help that much then why would X make all the effort to grab MTRRs on X86? - why would the kernel use BATs to map its memory? -- Linh Dang ** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/
