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Test results for Knights Landing
Author:  Date: 2016-11-27 00:45
Looks like a typo in the KNL recip-throughput number for FMA - it's currently 3. KNF and KNC get 1, and this chip is a real FMA machine - it's designed around that unit. Pretty sure the correct number for KNL is 0.5 (like VADDPS and VMULPS).

As for why the chip has 4 threads per core - I'm the guy that persuaded KNF (and thus KNC) to have 4 threads, and the reason is first to hide memory misses, second branch mispredicts, and third instruction latencies. Those are all huge bottlenecks in real-world performance. Yes, you can also hide them with huge OOO machines, wide decoders, and long pipelines, but when flops/watt is your efficiency metric, those aren't the first choice. The Knights line of chips already open the book with "we assume you have 70+ threads of stuff to do", and while getting from 1 thread to 4 is agony, and 4 threads to 16 is hard, getting from 70 threads to 280 is actually pretty simple.

 
thread Test results for Knights Landing new - Agner - 2016-11-26
reply Test results for Knights Landing new - Nathan Kurz - 2016-11-26
replythread Test results for Knights Landing - Tom Forsyth - 2016-11-27
reply Test results for Knights Landing new - Søren Egmose - 2016-11-27
last reply Test results for Knights Landing new - Agner - 2016-11-30
replythread Test results for Knights Landing new - Joe Duarte - 2016-12-03
replythread Test results for Knights Landing new - Agner - 2016-12-04
last reply Test results for Knights Landing new - Constantinos Evangelinos - 2016-12-05
last replythread Test results for Knights Landing new - John McCalpin - 2016-12-06
replythread Test results for Knights Landing new - Agner - 2016-12-06
last reply Test results for Knights Landing new - John McCalpin - 2016-12-08
last reply Test results for Knights Landing new - Joe Duarte - 2016-12-07
replythread Test results for Knights Landing new - zboson - 2016-12-28
last reply VZEROUPPER new - Agner - 2016-12-28
replythread Test results for Knights Landing new - Ioan Hadade - 2017-07-13
last reply Test results for Knights Landing new - Agner - 2017-07-13
last replythread INC/DEC throughput new - Peter Cordes - 2017-10-09
last reply INC/DEC throughput new - Agner - 2017-10-10