linux-kernel - Re: [PATCH 3/4] KVM: MMU: Make kvm_handle

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Message-ID: <4FE2DA5B.4080706@redhat.com>
Date:	Thu, 21 Jun 2012 11:24:59 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Takuya Yoshikawa <takuya.yoshikawa@...il.com>
CC:	Takuya Yoshikawa <yoshikawa.takuya@....ntt.co.jp>,
	mtosatti@...hat.com, agraf@...e.de, paulus@...ba.org,
	aarcange@...hat.com, kvm@...r.kernel.org, kvm-ppc@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] KVM: MMU: Make kvm_handle_hva() handle range of addresses

On 06/19/2012 04:46 PM, Takuya Yoshikawa wrote:
> On Mon, 18 Jun 2012 15:11:42 +0300
> Avi Kivity <avi@...hat.com> wrote:
> 
>> Potential for improvement: don't do 512 iterations on same large page.
>> 
>> Something like
>> 
>>     if ((gfn ^ prev_gfn) & mask(level))
>>         ret |= handler(...)
>> 
>> with clever selection of the first prev_gfn so it always matches (~gfn
>> maybe).
> 
> 
> I thought up a better solution:
> 
> 1. Separate rmap_pde from lpage_info->write_count and
>    make this a simple array. (I once tried this.)
> 

This has the potential to increase cache misses, but I don't think it's
a killer.  The separation can simplify other things as well.


> 2. Use gfn_to_index() and loop over rmap array:
>  ...
>   /* intersection check */
>   start = max(start, memslot->userspace_addr);
>   end = min(end, memslot->userspace_addr +
>                  (memslot->npages << PAGE_SHIFT));
>   if (start > end)
>       continue;
> 
>   /* hva to gfn conversion */
>   gfn_start = hva_to_gfn_memslot(start);
>   gfn_end = hva_to_gfn_memslot(end);
> 
>   /* main part */
>   for each level {
>       rmapp = __gfn_to_rmap(gfn_start, level, memslot);
>       for (idx = gfn_to_index(gfn_start, memslot->base_gfn, level);
>            idx < gfn_to_index(gfn_end, memslot->base_gfn, level); idx++) {
>               ...
>           /* loop over rmap array */
>           ret |= handler(kvm, rmapp + idx, data);
>       }
>   }
> 

Probably want idx <= gfn_to_index(gfn_end-1, ...) otherwise we fail on
small slots.

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


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