On 11/19/2013 11:38 AM, Linus Torvalds wrote:
> On Mon, Nov 18, 2013 at 8:37 PM, H. Peter Anvin <h...@zytor.com> wrote:
>>
>> Do you have a preference:
>>
>> 1. Considering the 32-bit truncation incidental (take it or leave it);
>> 2. Require the 32-bit truncation, or
>> 3. Get rid of it completely?
>
> I don't have a huge preference, but I hate the current situation (with
> Fenghua's patch) where it's not consistent. One path uses just 32-bits
> of the count (thanks to the "mov %edx,%ecx") while another path uses
> 64 bits.
>
> One or the other, but not a mixture of both.
>
> And only tangentially related to this: I do think that we could be
> stricter about the count. Make it oops if the high bits are set,
> rather than overwrite a lot of memory. So I would not be adverse to
> limiting the count to 31 bits (or even less) explicitly, and thus
> making the while 32-vs-64 bit issue moot.
>
I guess the question is if we want to spend the extra cycles on a test
and branch. For now I suggest that we just put back the truncation in
the form of a movl instruction.
-hpa
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