<p>I don't know if that helps, but here is a a trace I took with perf on the currently running 64-gaussian GMM: </p>

<pre><code>16.29%  spotter  libmkl_avx.so            [.] mkl_blas_avx_xdgemmger                                          
14.31%  spotter  spotter                  [.] arma::eglue_core&lt;arma::eglue_minus&gt;::apply&lt;arma::Mat&lt;double&gt;, arma::Mat&lt;double&gt;, arma::Glue&lt;arma::Col&lt;double&gt;, arma::Gen&lt;arma::Row&lt;double&gt;, arma::gen_ones&gt;, arma::glue_times&gt; &gt;                  
11.65%  spotter  libm-2.21.so             [.] __ieee754_exp_avx                                                 
11.57%  spotter  libmkl_avx.so            [.] mkl_blas_avx_dgemm_nocopy_anbn_meq9_keq9_b0
 6.72%  spotter  spotter                  [.] arma::op_dot::direct_dot&lt;double&gt;                               
 5.90%  spotter  spotter                  [.] arma::eglue_core&lt;arma::eglue_schur&gt;::apply&lt;arma::Mat&lt;double&gt;, arma::Mat&lt;double&gt;, arma::Glue&lt;arma::Gen&lt;arma::Col&lt;double&gt;, arma::gen_ones&gt;, arma::Op&lt;arma::eGlue&lt;arma::subview_col&lt;double&gt;, arma::Col&lt;double&gt;, arma::eglue_schur&gt;, arma::op_htrans&gt;, arma::glue_times&gt; &gt; 
 4.72%  spotter  libmkl_avx.so            [.] mkl_blas_avx_dgemm_kernel_0 
 4.61%  spotter  spotter                  [.] etl::detail::Assign&lt;float, etl::unary_expr&lt;float, etl::p_max_pool_p_transformer&lt;etl::binary_expr&lt;float, etl::unary_expr&lt;float, etl::rep_r_transformer&lt;etl::fast_matrix_impl&lt;float, std::array&lt;float, 12ul&gt;, (etl::order)0, 12ul&gt; const&amp;, 52ul, 12ul&gt;, etl::transform_op&gt;, etl::plus_binary_op&lt;float&gt;, etl::unary_expr&lt;float, etl::sub_view&lt;etl::fast_matrix_impl&lt;float, std::vector&lt;float, std::allocator&lt;float&gt; &gt;, (etl::order)0, 2ul, 12ul, 52ul, 12ul&gt;&amp;&gt;, etl::identity_op&gt; &gt;, 2ul, 2ul&gt;, etl::transform_op&gt;&amp;&gt;::operator()                                                               
 2.81%  spotter  libmkl_avx.so            [.] LAY16_M8_Tailgas_1
 2.39%  spotter  spotter                  [.] arma::Row&lt;unsigned long&gt;::operator= 
</code></pre>

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