On 06/04/18 12:13, George Dunlap wrote: > On Thu, Apr 5, 2018 at 6:11 PM, Juergen Gross <jgr...@suse.com> wrote: >>> Option 1: Put the RSDP in lowmem unless we know the guest will use the >>> address in start_info >>> Pro: Existing Linux instances boot >>> Con: Existing BSD instances whose memory is an exact multiple of 1 GiB >>> will have slightly slower TLB miss times. >> >> ... whose memory is >=1GiB ... > > No, the performance benefit only applies to sections of ram that are > complete 1GiB-aligned sections. If you have 1.75GiB, then the first > gigabyte will be a 1GiB page in the p2m (and get the performance > benefit) but the other 0.75GiB will be 2MiB aligned (and not).
Right. Moving the RSDP out of the first GiB will make it possible to map that area with a single 1 GiB page. > We can be pedantic and nail down exactly who will get what benefit > when, but all it will do is demonstrate how limited this performance > benefit is. Moving the shared_info page of HVM guests allowing large pages to be used increased HVM performance by several percent (e.g. munmap of user pages was up to 2 times faster this way). Juergen _______________________________________________ Xen-devel mailing list Xenemail@example.com https://lists.xenproject.org/mailman/listinfo/xen-devel