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Date: Sun, 5 Jun 2005 07:41:09 +0800
From: Steven Gong <steven.gong@gmail.com>
Reply-To: Steven Gong <steven.gong@gmail.com>
To: harmony-dev@incubator.apache.org
Subject: Re: JVM performance article
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On 6/4/05, Michael Hind <hindm@us.ibm.com> wrote:
>=20
> Instead, modern JVMs try to balance these compilation burps by using a
> strategy (selective optimization) that tries to ensure a method really is
> important enough to invoke the JIT on. This is often done by counting the
> number of times a method is called and is sometimes augmented with a loop
> count for the method (in case the method is called infrequently, but
> nevertheless a good chunk of execution time is spent in.) When this cheap
> profile indicates a method is important, the JIT is used to improve the
> generated code. Other systems use infrequent sampling (100/sec) of the
> call stack to find candidates to be JITed. Many such systems also use
> multiple levels of JIT optimizations (similar to a static compiler)
> depending on how important the method appears at runtime. Jikes RVM uses
> the sampling to plug into a simple cost/benefit model to determine what
> level (if any) of the JIT to use.


Is the sampling process done before running or during runtime? If it's done=
=20
during runtime, does it mean that some methods may be compiled several time=
s=20
by different leveled JIT?=20

--=20
Best Regards
Steven Gong

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