title: Do 128bit cross lane operations in AVX512 give better performance?
body: <p>In designing forward looking algorithms for AVX256, AVX512 and one day AVX1024 and considering the potential implementation complexity/cost of fully generic permutes for large SIMD width I wondered if it is better to generally keep to isolated 128bit operations even within AVX512?</p>
  
  <p>Especially given that AVX had 128bit units to execute 256bit operations.</p>
  
  <p>To that end I wanted to know if there was a performance difference between AVX512 permute type operations across all of the 512bit vector as opposed to permute type operations <em>within</em> each 4x128bit sub-vectors of a 512bit vector?</p>