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From Egor Pasko <egor.pa...@gmail.com>
Subject Re: [drlvm][vm, mmtk] adding thread-local storage functionality to vmmagic
Date Fri, 18 Aug 2006 05:43:33 GMT
On the 0x1C8 day of Apache Harmony Mikhail Fursov wrote:
> Egor,
> Why do you think we need to support platform specific issues in helpers? Is
> there any example that shows that we can't write a helper without reference
> platform details? 

It depends on how much of a helper code we want to write in Java. We
can always say: "hey, this is platform-dependent, let it be a whole
vmmagic and let JIT take care". If it is a large piece of code,
it is not good to code it down in JIT IR(s) and is better written in
Java. I think, we all agree here.

As a 1 more example ... maybe some day we decide to inline fast-path
of spinlocks. 

Which is a) a helper b) is platfrom-dependent. 

Implementing fast-path-spins in JIT IR is not a lot to do. But
specifying the interface and updating all components (JITs) to handle
that way of interaction on all platforms .. may make a burden. Coding
spin-locking in Java would make it difficult to write optimal (think of
explicitly parallel architectures...)

Both approaches seem to be quite complicated here. But all-in-JIT
approach seems to have more chances to be faster here.

Thus, it would be good to have both:
* vmmagic (inlined by JITs)
* helpers (partially) written in Java (using vmmagic)
and decide how fine-grained those magics should be depending on
specific situation.

> I think we should avoid #ifdef's in Java as much as we can.

Yes, my vision is the same. At least, until we come accross a large
piece of system-dependent code that is good to be inlined by JIT. I
think, it is not likely to happen, large pieces of code tend to work
longer :) and inlining them does not give so much benefit..

-- 
Egor Pasko, Intel Managed Runtime Division


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