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http://jira.codehaus.org/browse/RVM-341?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_113385 ]
Ian Rogers commented on RVM-341:
--------------------------------
It appears the best pair of copy instructions are movq to load and movntq to store. The movntq is an unordered store so at the end of the copy loop a sfence is necessary. Similarly (p)xor-ing a register and then using movntq is the best way to zero memory. We can assume SSE. It would be nice to know whether there's an advantage in interleaving SSE XMM register movq/ntq(s) with MMX MM register ones.
> 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: 2.9.3
>
>
> 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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