On Thu, Oct 15, 2009 at 04:33:11PM +0900, Avi Kivity wrote: > One way to improve the gfn_to_pfn() memslot search is to register just > one slot. This can only work on 64-bit, since even the smallest guests > need 4GB of physical address space. Apart from speeding up > gfn_to_page(), it would also speed up mmio which must iterate over all > slots, so a lookup cache cannot help. > > This would require quite a bunch of changes: > - modify gfn_to_pfn() to fail gracefully if the page is in the slot but > unmapped (hole handling) > - modify qemu to reserve the guest physical address space > - modify qemu memory allocation to use MAP_FIXED to allocate memory > - some hack for the vga aliases (mmap an fd multiple times?) > - some hack for the vmx-specific pages (e.g. APIC-access page) > > Not sure it's worthwhile, but something to keep in mind if a simple > cache or sort by size is insufficient due to mmio. Downside is you lose the ability to write protect a small slot only (could mprotect(MAP_READ) the desired area but get_log+write_protect must be atomic). Also if you enable dirty log for the large slot largepages are disabled. -- 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
