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[jira] Commented: (RVM-341) Improved copying in VM_Memory

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[ http://jira.codehaus.org/browse/RVM-341?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=178982#action_178982 ]

Ian Rogers commented on RVM-341:
--------------------------------

So we never really went very far with the games, ideally we'd have created a 128bit unboxed type and used that for the copies and batch up loads and stores. The furthest the games went were to recognize 64bit load and store pairs and optimize to use an XMM register. This may suffer a penalty on nehalem. Anyway, Intel have done all the work in nehalem and rep movs is the best instruction and even now tackles alignment problems (optimization manual 2.2.6). It would be trivial to create a magic to emit this instruction. Of course all of this is silly as the game changes for 64bits.

> Improved copying in VM_Memory
> -----------------------------
>
> Key: RVM-341
> URL: http://jira.codehaus.org/browse/RVM-341
> Project: RVM
> Issue Type: Improvement
> Components: Instruction Architecture: Intel, Runtime
> Reporter: Ian Rogers
> Fix For: 1000
>
> Attachments: memcpyTest.java, memcpyTestC.c
>
>
> r13857 improved memory copying for Intel with SSE2 so that we used 64bit copies rather than 32bit copies. This gave a large number of speed ups:
> http://jikesrvm.anu.edu.au/cattrack/results/rvmx86lnx32.anu.edu.au/perf/1790/performance_report
> most notably on SpecJBB 2000. There is a low-hanging fruit to improve this further, for example, by using 128bit copies and using more than 1 register to do the copying.

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