Re: [Xen-devel] [PATCH 2/4] x86: further speed-up to hweight{32, 64}()

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 31.05.19 at 21:23, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 31/05/2019 02:52, Jan Beulich wrote:
>> According to Linux commit 0136611c62 ("optimize hweight64 for x86_64")
>> this is a further improvement over the variant using only bitwise
>> operations. It's also a slight further code size reduction.
>>
>> Suggested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> 
> This should also include ARM64, which also unconditionally selects
> HAS_FAST_MULTIPLY in Linux.

I've very intentionally split the Arm change from the x86 one:
Looking at the generated code I'm unconvinced this is a win
there, and hence I'd prefer if someone could measure this. It
is for this reason that patch 3 was actually sent as RFC.

> As for the x86 side of things, Acked-by: Andrew Cooper
> <andrew.cooper3@xxxxxxxxxx>

Thanks.

Jan



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