[
https://issues.apache.org/jira/browse/QUICKSTEP-59?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15615587#comment-15615587
]
ASF GitHub Bot commented on QUICKSTEP-59:
-----------------------------------------
Github user saketj commented on the issue:
https://github.com/apache/incubator-quickstep/pull/114
Merged in master
> Improve performance of BitVector in Quickstep by eliminating branches
> ---------------------------------------------------------------------
>
> Key: QUICKSTEP-59
> URL: https://issues.apache.org/jira/browse/QUICKSTEP-59
> Project: Apache Quickstep
> Issue Type: Improvement
> Components: Query Execution, Utility
> Reporter: Saket Saurabh
> Assignee: Saket Saurabh
> Attachments: QUICKSTEP-59.01.patch
>
>
> The {{setBitRegularVersion()}} of {{BitVector.hpp}} is a critical function
> that is called in various tight loop iterations over storage blocks
> throughout the Quickstep code. This function has a simple purpose of setting
> a bit value in a BitVector to true/false given a boolean argument. However,
> it has an expensive if-else branch that can add a significant penalty at
> runtime due to branch mis-predictions.
> This short PR completely removes branching from the
> {{setBitRegularVersion()}} by replacing the same functionality with a set of
> bitwise arithmetic operations. Given that a branch mis-prediction costs about
> 10 cycles, the branchless code is expected to save those precious 10 cycles
> at the slight expense of 4 additional bitwise operations (an additional 2-4
> cycles only, given hyper-threading).
> *Tests:*
> The existing unit tests should already cover the changes introduced by this
> PR. Correctness also verified by comparing TPC-H query output results.
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
