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Message:

prog eating more CPU time.

Posted by gopi on June 01, 2000 at 5:00 AM

Bill,
I'm gopi from india. I want to know how debug when my program
takes up more cpu time & how could it be optimized. I'm working
in LINUX environment.

Expecting your reply. Thank you.
Regards,
gopi.

> > Bill,
> > Thanks for the informative article on Hotspot. One thing not covered is the actual cpu time Hotspot's profiler takes to work out where the hotspots are. Surely if this is excessive it could cancel out the benefits obtained from optimization. There is is also the overhead in dynamic compilation.

> True, in Hotspot you've got profiling going on and compilation
> to native, which are taking up CPU time. In a traditional JIT
> you also have compilation to native going on, which eats up CPU
> time.

> So the CPU time spent doing this processing has to be recouped
> in faster execution time, otherwise it's not worth doing the
> processing in the first place. This is why they say that Hotspot
> has more time to do a better job of optimization during the
> compilation to native compared to a traditional JIT. Since
> Hotspot is only converting and optimizing say 10 to 20 percent
> of the methods to native, it has more time to spend on each
> method.

> Sun didn't say what percentage of time their Hotspot VM spends
> doing profiling. I didn't ask them that, so they might have an
> answer to give out, but they might say that details like that
> are proprietary. What we do know is that they would have to make
> the CPU time spent profiling a good investment which returns
> more CPU time later in the form of faster program execution.

> To me it seems like finding the optimum tradeoff between
> time spend profiling (and compilation/optimizing) and
> increased execution speed would be quite tricky, and would
> require a lot of empirical measuring and ingenuity. When we
> finally get to see Hotspot for ourselves, we'll find out how
> well they did initially. I expect Sun to be able to improve
> this tradeoff over time, from release to release, as they get
> more empirical information and more time to think up and try
> out various tweaks to their algorithms.

> bv