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I really don't want to write a JIT/AOT myself

Odin Zeno
Note: This was originally posted on 11th August 2010 at http://forums.arm.com

It seems that I have to raise the chip performance through this way, and I was acknowledged of Ubuntu recently got some from arm.
I don't want to spent time uselessly at writing the samething again(wasting your time or mine). But can that JIT/AOT work on a chip with less than 20 KB ram? Is there anyone know the detail? Some article said it boosts speed to 14X, is that true?
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    Note: This was originally posted on 12th August 2010 at http://forums.arm.com

    > But can that JIT/AOT work on a chip with less than 20 KB ram?


    Well it really depends doesn't it =)

    What are you jitting from, what do you want to JIT in to, how much code are you jitting, what kind of optimization are you after?

    How much support code does the language need?

    Can you do a 100% JIT, or will you have to fallback on an interpreter in some cases? [it is rare for a JIT to JIT everything]

    In all honestly 20KB of RAM is not much if you have a "typical JIT" - assuming you can load the bytecode from Flash, then you need space for: output JIT'ted code, the JIT itself, any interpreter support, two stacks (one for JIT/interperter and one for code), and then any data your program is actually using.

    If you can restrict the bytecode to something simple (relatively flat mapping to the hardware ISA), and have a design with a very limited support library then it could be done. This type of micro-bytecode has found use in some boot-strap type code in many devices (BIOS chipsets often run a bytecode). Assuming you want to JIT something like full Java, then probably not possible in 20K, but then I've never really tried either.
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  • 0
    Note: This was originally posted on 12th August 2010 at http://forums.arm.com

    > But can that JIT/AOT work on a chip with less than 20 KB ram?


    Well it really depends doesn't it =)

    What are you jitting from, what do you want to JIT in to, how much code are you jitting, what kind of optimization are you after?

    How much support code does the language need?

    Can you do a 100% JIT, or will you have to fallback on an interpreter in some cases? [it is rare for a JIT to JIT everything]

    In all honestly 20KB of RAM is not much if you have a "typical JIT" - assuming you can load the bytecode from Flash, then you need space for: output JIT'ted code, the JIT itself, any interpreter support, two stacks (one for JIT/interperter and one for code), and then any data your program is actually using.

    If you can restrict the bytecode to something simple (relatively flat mapping to the hardware ISA), and have a design with a very limited support library then it could be done. This type of micro-bytecode has found use in some boot-strap type code in many devices (BIOS chipsets often run a bytecode). Assuming you want to JIT something like full Java, then probably not possible in 20K, but then I've never really tried either.
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