Re: [Xen-devel] [PATCH v4 1/4] x86: use PDEP/PEXT for maddr/direct-map-offset conversion when available

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Tue, Sep 18, 2018 at 06:36:21AM -0600, Jan Beulich wrote:
> This allows to fold 6 instructions into a single one, reducing code size
> quite a bit, especially when not considering the fallback functions
> (which won't ever need to be brought into iCache or their mappings into
> iTLB on systems supporting BMI2).
> 
> Make use of gcc's new V operand modifier, even if that results in a
> slightly odd dependency in the sources (but I also didn't want to
> introduce yet another manifest constant). This assumes that backports of
> support for this relatively new modifier have only been done to tool
> chains with not too old a binutils (gas) version. If this turns out to
> be a false assumption, we'll have to add HAVE_AS_BMI2 as a qualifier.
> 
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

I'm afraid this patch series smells like  "micro optimisation gone too
far" to me. :-/

Wei.

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