Re: [Xen-devel] [PATCH 2/9] x86/mtrr: drop mtrr_if indirection

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 18/08/16 02:59, Doug Goldstein wrote:
> On 8/17/16 7:49 AM, Jan Beulich wrote:
>>>>> On 17.08.16 at 01:28, <cardoe@xxxxxxxxxx> wrote:
>>> There can only ever be one mtrr_if now and that is the generic
>>> implementation
>> This is only true when taking into consideration that cpu_has_mtrr
>> is #define-d to 1 right now. I'm not sure that's actually a good
>> assumption (especially when think about running Xen itself
>> virtualized, or possibly adding a mode of operation where no MTRRs
>> are to be used). But if we want to keep it that way, then I'd suggest
>> this patch should include removing cpu_has_mtrr (which will then
>> show to the reviewers that the checks of mtrr_if against NULL
>> indeed are dead code.
> Sure I can remove cpu_has_mtrr that would certainly make it cleaner. Is
> it ok with you and Andrew to make the assumption that we'll always have
> MTRRs (until the day we don't like you described)?

Please don't remove cpu_has_mtrr.  I plan to make better use of it with
the future plan to move PV guests into a PVH container.

In such a case, the PVH container won't want/need MTRRs, and we will get
better performance by not having them available.

~Andrew

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