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From "Tim Armstrong (Code Review)" <ger...@cloudera.org>
Subject [Impala-ASF-CR] IMPALA-5988: optimise MemPool::TryAllocate()
Date Wed, 04 Oct 2017 19:41:58 GMT
Tim Armstrong has posted comments on this change. ( http://gerrit.cloudera.org:8080/8145 )

Change subject: IMPALA-5988: optimise MemPool::TryAllocate()
......................................................................


Patch Set 3:

(2 comments)

http://gerrit.cloudera.org:8080/#/c/8145/3/be/src/runtime/mem-pool.h
File be/src/runtime/mem-pool.h:

http://gerrit.cloudera.org:8080/#/c/8145/3/be/src/runtime/mem-pool.h@122
PS3, Line 122:   uint8_t* TryAllocateUnaligned(int64_t size) noexcept {
> Change lgtm. Mind explaining the original motivation behind the 8-byte defa
The default has been 8 byte aligned for as long as I'm aware. 
I added the alignment parameter because there was a case where we needed 16-byte alignment

I think 8-byte alignment is a reasonable default and matches what malloc() does. There's sometimes
a perf benefit (although it's pretty limited on recent Intel processors). It might make sense
to use unaligned memory in some other cases but it'd probably need perf validation.


http://gerrit.cloudera.org:8080/#/c/8145/3/be/src/runtime/mem-pool.h@123
PS3, Line 123: Allocate<true>(size, 1);
> TryAllocateAligned(size, 1);
This was somewhat deliberate - I wanted to force inlining into this function so that the alignment
logic could be optimised out. Added a comment - lmk if that addresses the comment.



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Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-MessageType: comment
Gerrit-Change-Id: I088012084fe535a67a3cd1103ced5a02027f961a
Gerrit-Change-Number: 8145
Gerrit-PatchSet: 3
Gerrit-Owner: Tim Armstrong <tarmstrong@cloudera.com>
Gerrit-Reviewer: Alex Behm <alex.behm@cloudera.com>
Gerrit-Reviewer: Dan Hecht <dhecht@cloudera.com>
Gerrit-Reviewer: Tim Armstrong <tarmstrong@cloudera.com>
Gerrit-Comment-Date: Wed, 04 Oct 2017 19:41:58 +0000
Gerrit-HasComments: Yes

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