luke warm methods?

[Ben Evans]

hotspot-dev-bounces at openjdk.java.net wrote on 22/04/2010 00:42:28:

> We decay counters periodically since over time counters should only 
> go up so maybe that's the problem.  If you run with -XX:-
> UseCounterDecay it will turn it off but all the other flags that 
> control it aren't available in product mode. This is certainly one 
> of the pathologies of an invocation counter based system with 
> relatively high thresholds. 

Just so I'm clear, this doesn't affect the compiled status of methods, 
right?

What's being discussed here is that if an initial burst of activity 
results in a method being called say 4096 times (vs a threshold of 10000), 
then after 1 minute, then that method has had its invocation counter 
reduced to 1024. 

So the usual scenario whereby HotSpot reaches a steady state in terms of 
compilation activity can be disrupted by a sudden flurry of activity on 
rarely-used methods (which will be effectively cold due to the decay 
process), which pushes the invocation counts of these methods above 
compilation threshold. If these methods then go quiet again, then HS will 
*not* deoptimize and drop these methods back to interpreted mode, even if 
their invocation counters subsequently decay below threshold. Correct?

Thanks,

Ben
-- 
Ben Evans
GFFX Auto Trading
Deutsche Bank, London
Office: +44 (0)20 7541 3953


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