Re: [dpdk-dev] [PATCH v6 0/8] fib: implement AVX512 vector lookup

[Thomas Monjalon <thomas@monjalon.net>]

14/07/2020 16:38, Stephen Hemminger:
> "Kinsella, Ray" <mdr@ashroe.eu> wrote:
> > On 13/07/2020 23:19, Stephen Hemminger wrote:
> > > Did anyone else see the recent AVX512 discussion from Linus:
> > >   "I hope AVX512 dies a painful death, and that Intel starts fixing real problems 
> > >    instead of trying to create magic instructions to then create benchmarks that they can look good on.   
> > 
> > Yup - I saw this one.
> > Sweeping statements like these are good to provoke debate, the truth is generally more nuanced.
> > If you continue to read the post, Linus appears to be mostly questioning microprocessor design decisions.
> > 
> > That is an interesting discussion, however the reality is that the technology does exists and may be beneficial for Packet Processing. 
> > 
> > I would suggest, we continue to apply the same logic governing adoption of any technology by DPDK. 
> > When the technology is present and a clear benefit is shown, we use it with caution.
> > 
> > In the case of Vladimir's patch,
> > the user has to explicitly switch on the AVX512 lookup with RTE_FIB_DIR24_8_VECTOR_AVX512.
> 
> Using what is available makes sense in DPDK. 

Why does it require explicit  enabling in application?
AVX512 is not reliable enough to be automatically used when available?