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From "Rei Odaira (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-11519) Add support for IBM POWER
Date Wed, 15 Jun 2016 21:23:09 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-11519?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15332607#comment-15332607
] 

Rei Odaira commented on CASSANDRA-11519:
----------------------------------------

Hi,

The linked document says PowerPC does not support unaligned 64-bit floating-point access in
the hardware, but it also says PowerPC supports hardware-based unaligned integer access. As
far as I understand, all of the unaligned accesses in Memory.java, MemoryUtil.java, and FastByteOperations.java
are for integers.

Actually, the linked document is quite old (written in 2005). The latest POWER8 processor,
released two years ago, supports hardware-based unaligned access for every combination of
32-bit/64-bit integer/floating-point numbers. In my measurement, there is no measurable performance
penalty in unaligned access, compared with aligned access. The only exception is access  that
crosses a page boundary, which is 10x slower than normal access, but it is also the case in
x86.

If you need to know the situation in POWER7 and older processors, I'll investigate them. There
are some other implementations of the POWER architecture (e.g. for game consoles), but I believe
POWER8, which is targeting the server market, is the only POWER implementation that practically
runs Cassandra.

> Add support for IBM POWER
> -------------------------
>
>                 Key: CASSANDRA-11519
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-11519
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>         Environment: POWER architecture
>            Reporter: Rei Odaira
>            Assignee: Rei Odaira
>            Priority: Minor
>             Fix For: 2.1.x, 2.2.x, 3.0.x, 3.x
>
>         Attachments: 11519-2.1.txt, 11519-3.0.txt
>
>
> Add support for the IBM POWER architecture (ppc, ppc64, and ppc64le) in org.apache.cassandra.utils.FastByteOperations,
org.apache.cassandra.utils.memory.MemoryUtil, and org.apache.cassandra.io.util.Memory.



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