Summit comment on interference between hot vs. cold code
rasbold at google.com
Fri Sep 18 11:37:33 PDT 2009
On Fri, Sep 18, 2009 at 10:50 AM, John Rose <John.Rose at sun.com> wrote:
> This just came up during Q&A on Christian Wimmer's talk
> http://wiki.jvmlangsummit.com/Trace-based_JIT , and I want to capture it
> in this forum.
> Library writers (like Martin Buchholz) do not want to be burdened with
> factoring (sequestering) cold from hot code in order to get good
> optimization. Trace-based compilation sifts input code naturally.
> A root cause in Hotspot of the interference between cold and hot code
> (besides whole-method compilation per se) is the poor metrics we use for
> inlining. In particular, we fail to inline a method if it look too large
> (in absolute bytecode count) even if most of its bytecodes are never
> Now that we have a bytecode summarization mechanism (for escape analysis)
> perhaps we could measure inline candidates more accurately, by counting
> their "weight" only according to actually executed (or frequently executed)
> Also, once a whole method is being compiled, we should be corresponding
> more eager to inline from hot call sites than from cold ones.
Can you elaborate on the last statement a little bit? I don't think I
understand what you mean....
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