<story><title>Erlang and IBM Power8 in the cloud: super-high single-system parallelism</title><url>http://erlang.org/pipermail/erlang-questions/2014-October/081407.html</url></story><parent_chain><item><author>throwaway_yy2Di</author><text>How does POWER8 compare to x86, e.g. Haswell? Just skimming some of the architecture details...&lt;p&gt;* 4x hardware threads per core (8-way SMT vs. 2)&lt;p&gt;* 1&amp;#x2F;4th FP throughput per core (8 SP flops&amp;#x2F;cycle vs. 32)&lt;p&gt;* 3x bandwidth to RAM (230 GB&amp;#x2F;s vs. 68) [edit: updated for Haswell-EP]&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/POWER8#Specifications&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;en.wikipedia.org&amp;#x2F;wiki&amp;#x2F;POWER8#Specifications&lt;/a&gt;&lt;p&gt;&lt;a href=&quot;http://www.redbooks.ibm.com/abstracts/tips1153.html&quot; rel=&quot;nofollow&quot;&gt;http:&amp;#x2F;&amp;#x2F;www.redbooks.ibm.com&amp;#x2F;abstracts&amp;#x2F;tips1153.html&lt;/a&gt;&lt;p&gt;What is it good for?</text></item></parent_chain><comment><author>nkurz</author><text>IBM has solid documentation of more of the Power8 details here: &lt;a href=&quot;http://www.setphaserstostun.org/power8/POWER8_UM_external_22APR2014_pub.pdf&quot; rel=&quot;nofollow&quot;&gt;http:&amp;#x2F;&amp;#x2F;www.setphaserstostun.org&amp;#x2F;power8&amp;#x2F;POWER8_UM_external_22...&lt;/a&gt;&lt;p&gt;Going only by specs, it seems that in many other cases each Power8 core has about 2-4x the resources of a Haswell core:&lt;p&gt;&lt;pre&gt;&lt;code&gt;  64KB vs 32KB L1D
  512KB vs 64KB L2
  8MB vs 2.5MB L3
  16 vs 10(?) outstanding L1 requests
  8 vs 4 instructions issued per cycle
  2 vs 1 stores per cycle (or 4 vs 2 loads if no stores)
  3 vs 4&amp;#x2F;5 cycle L1 latency for 64-bit data
  5 vs 6&amp;#x2F;7 cycle L1 latency for vector data
  2048 vs 512 TLB entries (integrated with huge pages)
&lt;/code&gt;&lt;/pre&gt;
Specs that aren&amp;#x27;t higher than Haswell are usually the same --- skimming, I haven&amp;#x27;t found any that are lower.   This makes me think that a 4xSMT or 8xSMT Power8 core will probably be about equivalent to a 2xSMT (hyperthreaded) Haswell core.   Dedicated core operation (non-hyperthreaded) will vary more based on workload, but likely be 1x to 2x in favor of Power8.
But these are guesses based on written specs -- I&amp;#x27;m eager to see more real benchmarks.</text></comment>
<story><title>Erlang and IBM Power8 in the cloud: super-high single-system parallelism</title><url>http://erlang.org/pipermail/erlang-questions/2014-October/081407.html</url></story><parent_chain><item><author>throwaway_yy2Di</author><text>How does POWER8 compare to x86, e.g. Haswell? Just skimming some of the architecture details...&lt;p&gt;* 4x hardware threads per core (8-way SMT vs. 2)&lt;p&gt;* 1&amp;#x2F;4th FP throughput per core (8 SP flops&amp;#x2F;cycle vs. 32)&lt;p&gt;* 3x bandwidth to RAM (230 GB&amp;#x2F;s vs. 68) [edit: updated for Haswell-EP]&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/POWER8#Specifications&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;en.wikipedia.org&amp;#x2F;wiki&amp;#x2F;POWER8#Specifications&lt;/a&gt;&lt;p&gt;&lt;a href=&quot;http://www.redbooks.ibm.com/abstracts/tips1153.html&quot; rel=&quot;nofollow&quot;&gt;http:&amp;#x2F;&amp;#x2F;www.redbooks.ibm.com&amp;#x2F;abstracts&amp;#x2F;tips1153.html&lt;/a&gt;&lt;p&gt;What is it good for?</text></item></parent_chain><comment><author>jedbrown</author><text>&amp;gt; 9x bandwidth to RAM (230 GB&amp;#x2F;s vs. 25.6)&lt;p&gt;Haswell-EP supports 4 DDR4-2133 channels, or 68 GB&amp;#x2F;s (theoretical).  TDP on POWER8 is almost double and it&amp;#x27;s much more expensive, so we should think about it as having perhaps double the DRAM bandwidth (still excellent).&lt;p&gt;Note that POWER8 gets this bandwidth through many more channels, which favors the use of many memory streams.  This has been the case historically, with POWER favoring data structures that result in many streams, while the same transformation has been catastrophic for memory performance on Blue Gene&amp;#x27;s PPC, with its limited prefetch engine and small number of outstanding memory requests.</text></comment>