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Posted to issues-all@impala.apache.org by "Daniel Becker (JIRA)" <ji...@apache.org> on 2019/06/28 10:26:00 UTC
[jira] [Created] (IMPALA-8726) Autovectorisation leads to worse
performance in bit unpacking
Daniel Becker created IMPALA-8726:
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Summary: Autovectorisation leads to worse performance in bit unpacking
Key: IMPALA-8726
URL: https://issues.apache.org/jira/browse/IMPALA-8726
Project: IMPALA
Issue Type: Improvement
Reporter: Daniel Becker
Attachments: no_vector.png
The compiler (GCC 4.9.2) autovectorises bit unpacking for bit widths 1, 2, 4 and 8 (function BitPacking::UnpackValues), but this leads to actually worse performance (see the attached graph). We should consider whether it is worth disabling autovectorisation for bit unpacking, but future compiler versions may do a better job.
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