Michael S (already5chosen.delete@this.yahoo.com) on July 31, 2018 3:00 pm wrote:
> David Kanter (dkanter.delete@this.realworldtech.com) on January 3, 2014 12:58 am wrote:
> > Happy new year everyone - I thought I'd welcome in 2014
> > with a new and intriguing article on Knights Landing:
> >
> > The 14nm Knights Landing leverages Intel’s resources with a laser-like focus on HPC to deliver
> > a massive improvement over the previous generation. The building block of this architecture
> > is a pair of Silvermont-inspired CPUs with wide vector units and most importantly, a brand new
> > cache hierarchy, on-die fabric, and system infrastructure that is shared with Skylake. This
> > article is an in-depth analysis and prediction of the Knights Landing architecture.
> >
> > Read more in the full article on Knights Landing.
> >
> > As always, comments and questions are encouraged!
> >
> > David
>
> Select Intel® Xeon Phi™ Processors:
> 7210, 7210F, 7230, 7230F, 7250, 7250F,7290, and 7290F,
> PCN 116378-00, Product Discontinuance,
> End of Life
> https://qdms.intel.com/dm/i.aspx/9C54A9A7-BF37-4496-B268-BD2746EA54D3/PCN116378-00.pdf
>
> Barely lasted 2 years.
>


If the processors would be able to reach the same percentage of the peak speed, then Xeon Phi would have 1/2 of the performance per watt of NVIDIA Volta while Xeon Platinum would have 1/3 of the performance per watt of NVIDIA Volta.


(Off topic, while GPUs are without doubt the most efficient, the ratio 1/3, which was valid for the last several generations of Intel & NVIDIA is very far from the ridiculous ratios, such as 100, which were claimed in all the early propaganda papers about GPGPU.)


Nevertheless, the very little information that I have seen about the real speed attainable by Xeon Phi, suggest that in fact the percentage of the peak speed reached by Xeon Phi is around 2/3 of the percentage reached by Xeon Platinum. Therefore the real performance per watt is about the same for both.


Then the only advantage remaining for Xeon Phi is that, at the official prices, its performance per dollar is much better than for NVIDIA Volta and for Xeon Platinum or Gold.

This is offset by the reports that claim that optimizing programs for Xeon Phi is much more difficult than for the alternatives.


Since Xeon Phi does not appear to have enough advantages over its competitors, there is no surprise in the end-of-life announcements and in the Intel roadmaps which show that the successors of Xeon Phi will be high-core-count MCM derivatives of the mainstream Xeon Scalable products.



Still, it is not clear for me why this has ended so. There seems nothing wrong about the concept that a throughput-optimized processor should have a large number of dual-issue in-order cores with large SIMD units. This seems the obvious way to get high performance per watt and per dollar.


The main problem with Xeon Phi, its difficulties in reaching high percentages of its peak speed, do not seem related with the general concept, but seem to have been caused by various implementation quirks of Knights Landing.

At least this is what I have seen in the few published analyses of its microarchitecture, e.g. that from Agner Fog.



Has anyone of you seen any papers which analyse the causes of inefficiency in Xeon Phi ?




I believe that maybe the failure of Xeon Phi was caused by its design by a B team and by the rush to market of an immature implementation.


I think that it is bad that the failure of Xeon Phi has tainted this idea. For me, the ideal computer would be a 2-socket machine, where one socket would have a 2-core or 4-core 5 GHz OOOE processor, but the other socket would have very-high-core-count throughput-optimized processor, similar to Xeon Phi.

This arrangement would avoid the problems which appear when you mix low-latency cores with high-throughput cores in a single socket, when the extra heat caused by AVX-256 or AVX-512 force the use of a lower clock frequency, which slows down the threads where single-thread performance is important.