>Dong, Eddie wrote: >> Current shadow code do prefetch in FNAME(prefetch_page), but >it is only >> used >> to choose shadow_notrap_nonpresent_pte or shadow_trap_nonpresent_pte. >> >> At least for L1 shadow, prefetching to get exact shadow L1 pte won't >> cause >> performance regression (though handling time increases >slightly ) since >> it >> won't generate a new write protected page. >> >> >I'm not sure that "slightly" is accurate, we need to fetch 512 or 1024 >entries. On the other hand, we have the benefit of batching >(a call to >get_user_pages() with n = 512 is much faster than 512 calls. I think
Yes, that means we have to copy the guest page to kernel buffer. >that this will improve fork()s, but reduce performance with >sparsely-accessed memory maps, or with fork() followed by exec() >immediately. I saw pf_fixed reduced. Specifically the shadow fault is reduced, but overal perf gain with kernel build is minor. > >Only benchmarking can tell if it is an overall win. > >Xen limits the prefetch to a subset of the pages, maybe that's >a better >approach. > > >> for those L2+ shadow page tables, we can do similar for those pointed >> gfn which >> is already shadowed > >I think L2s are very rare compared to L1 page tables, so any benefit >would be minor. > Agree it happens rare. Eddie ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2005. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
