Github user srowen commented on a diff in the pull request:
https://github.com/apache/spark/pull/18551#discussion_r126657632
--- Diff: docs/ml-guide.md ---
@@ -61,6 +61,12 @@ To configure `netlib-java` / Breeze to use system
optimised binaries, include
project and read the [netlib-java](https://github.com/fommil/netlib-java)
documentation for your
platform's additional installation instructions.
+The most popular native BLAS such as [Intel
MKL](https://software.intel.com/en-us/mkl),
[OpenBLAS](http://www.openblas.net), are based on multi-threading, which will
conflict with Spark.
+
+If using a native BLAS based on multi-threading, you might get better
performance to set it to use single thread first
([SPARK-21305](https://issues.apache.org/jira/browse/SPARK-21305)).
--- End diff --
I might say, "Configuring these BLAS implementations to use a single thread
for operations may actually improve performance (see ...). It is usually
optimal to match this to the number of cores each Spark task is configured to
use, which is 1 by default and typically left at 1."
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