]]>
See:
A benchmark for accelerators. All the big boys seem to be on the chart. Step forwards Epiphany!!
tery
Statistics: Posted by greytery — Wed Mar 19, 2014 9:54 am
]]>
]]>
]]>
]]>
]]>
]]>
]]>
]]>
]]>
]]>
@eoghanoh - a couple of thoughts on your posts ..
You refer to shodruk's excellent and exciting demo: "if it scales linearly (as shodruk's mandelbrot demo shows)".
Shodruck writes that his multi-core timing results show that the application is not linear, but near linear.
Using Amdahl's equation to make a guess at the application seriality, it shows a small seriality factor as core numbers increase.
Playing with the numbers, extrapolating up to 64 and then on up to 1024, 4096 (er, I mean 4095) cores shows that this tiny serial component would be significant at the higher values. Theoretically though, it's still an impressive speedup, and that's before looking at the energy costs.
(I'm breaking a Golden Rule of performance engineering here: "Interpolate not extrapolate", but this is just for fun, OK)
You also show numbers for your application runs on the i7. Charting your results shows a huge tail-off as the effects of seriality and coherence (see N.Gunther) kick in from the Hyperthreading chip and operating system. If you tried this on someone's larger 12 (Hyperthreading) CPU Intel machine it's likely that you would not get much more speedup.
(I've worked on the performance of large Xeon and Hyperdome systems, which go up to a couple of hundred cores, and shown that real speedup curves can actually be negative at higher core numbers! Mileage varies considerably with the application).
As and when you recode/rerun for Epiphany, it's likely that the coherence effects will be considerably less - as has been said, bare metal, less Windoze or Linuzzz to get in the way - but there will still be some seriality which becomes significant at higher CPU numbers.
So I don't think there is "any hope of linear speedup". Near, but no cigar.
Looking forward to any results you may get if/when you get access to the chips. This is exactly the sort of games I intend to play myself.
tery
Statistics: Posted by greytery — Thu Jan 16, 2014 11:52 pm
]]>
]]>
]]>
]]>