Re: [benchmark] 1% performance overhead of paravirt_ops on nativekernels

[Avi Kivity]

Ingo Molnar wrote:
> Fork is pretty much the worst-case measurement for larger pte 
> overhead, as it has to copy around a lot of pagetables.
>   

We could eliminate that if we use the R/W bit on pgd entries.  fork() 
would be 256 clear_bit()s (1536 and 768 on i386 pae and nonpae).

copy_one_pte() disagrees though:

       if (unlikely(!pte_present(pte))) {
               if (!pte_file(pte)) {
                       swp_entry_t entry = pte_to_swp_entry(pte);

                       swap_duplicate(entry);
                       /* make sure dst_mm is on swapoff's mmlist. */
                       if (unlikely(list_empty(&dst_mm->mmlist))) {
                               spin_lock(&mmlist_lock);
                               if (list_empty(&dst_mm->mmlist))
                                       list_add(&dst_mm->mmlist,
                                                &src_mm->mmlist);
                               spin_unlock(&mmlist_lock);
                       }
                       if (is_write_migration_entry(entry) &&
                                       is_cow_mapping(vm_flags)) {
                               /*
                                * COW mappings require pages in both parent
                                * and child to be set to read.
                                */
                               make_migration_entry_read(&entry);
                               pte = swp_entry_to_pte(entry);
                               set_pte_at(src_mm, addr, src_pte, pte);
                       }
               }
               goto out_set_pte;
       }


Not sure how we can enlaze this thing.

--
error compiling committee.c: too many arguments to function

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