On Thu, Oct 15, 2009 at 02:46:38PM +0200, Alexander Graf wrote: > > On 15.10.2009, at 09:33, 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. > > One thing I've been wondering for quite a while is that slot loop. Why > do we loop over all possible slots? Couldn't we just remember the max > extry (usually 1 or 2) and not loop MAX_SLOT_AMOUNT times? > > That would be a really easy patch and give instant speed improvements > for everyone. gfn_to_memslot_unaliased uses kvm->nmemslots which is the max entry. Oh, kvm_is_visible_gfn does not. It should just use gfn_to_memslot_unaliased. -- 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
