Github user michaelkamprath commented on a diff in the pull request:
https://github.com/apache/spark/pull/16403#discussion_r94257179
--- Diff: common/unsafe/src/main/java/org/apache/spark/unsafe/Platform.java
---
@@ -244,6 +251,18 @@ public static void throwException(Throwable t) {
LONG_ARRAY_OFFSET = _UNSAFE.arrayBaseOffset(long[].class);
FLOAT_ARRAY_OFFSET = _UNSAFE.arrayBaseOffset(float[].class);
DOUBLE_ARRAY_OFFSET = _UNSAFE.arrayBaseOffset(double[].class);
+
+ // determine whether double access should be aligned.
+ String arch = System.getProperty("os.arch", "");
+ if (arch.matches("^(arm|arm32)")) {
--- End diff --
@kiszk I have tested on ARM 64 (`aarch64`). [Any alignment works for double
access
there](http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.den0024a/ch08s02.html),
though 8-byte aligned access looks to be about 10% faster than unaligned
access. Using an intermediate long buffer (your idea) is about 5% slower than
direct access regardless of being aligned or not. In both cases, I tested with
an ODROID C2 using Oracle Java 8.
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