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Re: [rvm-research] Slots and Object Barriers

by Ian Rogers (nabble) :: Rate this Message:

Hi Cristian,

the barrier options are a legacy of the barriers friend or foe paper - this is the best place to read about their trade-offs, although the analysis is now quite dated and some of the barriers are shown to improve application performance compared to no barriers! The card mark barriers never made it into, or were removed from, Jikes RVM. This chimes with the general "remove anything we don't want to support" attitude of Jikes RVM and this attitude is the reason d'etre for the MRP project [1]. Card mark barriers are issue MRP-21 [2]. Discontiguous spaces are much less of an issue with 64bit address spaces and MRP is the only Jikes RVM based platform to provide 64bit address spaces on Intel hardware. More issues with barriers are being exposed by our ongoing integration of the JUnicorn Java OS foundation into MRP.

Regards,
Ian

[1] http://mrp.codehaus.org/
[2] http://jira.codehaus.org/browse/MRP-21

2009/6/26 Cristian Perfumo <cperfumo@...>

Hi everybody,

Looking at org.mmtk.plan.generational.Gen, I see these constants:

public static final boolean USE_OBJECT_BARRIER_FOR_AASTORE = false; // choose between slot and object barriers
public static final boolean USE_OBJECT_BARRIER_FOR_PUTFIELD = false; // choose between slot and object barriers

I notice that if they are set to true, the applications go faster in general. I was wondering what the tradeoff is, if any, between having them set to true and false.

Also, I'm curious about the tradeoff between USE_DISCONTIGUOUS_NURSERY true and false.

The only place where they are tested is org.mmtk.plan.generational.GenMutator, in the fastPath(...) method.

Is there any place where I can read what the difference is between using slots and object barriers?

Thank you very much.

Cristian.

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