Re: [Qemu-devel] [PATCH] tcg/ppc: Add vector opcodes

[Richard Henderson]

On 2/22/19 9:13 AM, Mark Cave-Ayland wrote:
> On 22/02/2019 05:59, Richard Henderson wrote:
> 
>> This requires VSX, not just Altivec, so Power7 or later.
>>
>> Signed-off-by: Richard Henderson <address@hidden>
>> ---
>>
>> At present there are no tunables that can avoid the 64-bit element
>> load/store requirement.  As with requiring AVX1 for x86 hosts, I'm
>> not sure it's worth inventing such a tunable for pre-power7 hosts.
>>
>> Tested vs aarch64 risu test cases.  It's probably worth testing
>> this vs Mark's target/ppc conversion.
> 
> Oooh this looks really exciting! However... I only have a G4 Mac Mini around 
> that I
> use for testing which is Altivec-only :(  Is it much work to support non-VSX 
> hosts?

Hmm, dunno.  I'll think about it.

> This leads me to a related point that came up when Howard and I were testing 
> the PPC
> vector patches - how do we know at runtime which optimisations were being 
> used, e.g.
> what is the value of have_avx2 on a particular CPU running QEMU?

There is no way from within qemu itself.

> Under Linux this isn't too bad since you can just do "cat /proc/cpuinfo | 
> grep avx2"
> but it becomes more tricky when getting bug reports from Windows users who 
> aren't
> particularly technical...

Something like:
https://www.intel.com/content/www/us/en/support/articles/000005651/processors.html

or any one of several other utilities that can display cpuid information.


r~