Review Request for 6878481: Add performance counters in the JDK

[David Holmes - Sun Microsystems]

Hi Mandy,

Mandy Chung said the following on 09/03/09 05:25:
> This is related to 6857194: Add hotspot new perf counters to aid class 
> loading performance measurement.
> 
> It's useful to add performance counters in the library code so that perf 
> data from the JDK and VM can be collected and output in a unified way 
> (written in the jvmstat shared memory buffer).  I add a simple 
> sun.misc.PerfCounter class to maintain the list of perf counters for the 
> library to use.  This fix only instruments the class loading and jar/zip 
> to collect simple basic metrics.   Additional perf counters will be 
> added in the future.
> 
> Webrev:
>     http://cr.openjdk.java.net/~mchung/6878481/webrev.00/

What is the performance overhead here? This seems like a lot of extra 
code if you don't want to read the counters. Is there not some way to 
only conditionally enable them?

We're sticking in a lot of System.nanoTime() calls and on some systems 
it isn't necessarily cheap eg Windows - see 6440250. Even if it is 
cheap, there are potentially a lot of them in classloading intensive 
situations.

David