Review Request for 6878481: Add performance counters in the JDK
forax at univ-mlv.fr
Thu Sep 3 02:48:09 PDT 2009
Le 03/09/2009 10:54, Alan Bateman a écrit :
> Mandy Chung wrote:
>> 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.
> It's good to see the use of the instrumentation buffer extended to the
> I'm not sure how sun.misc.Perf behaves when running with
> -XX:-UsePerfData. You've probably checked this anyway, but just in
> It would be good to include a comment to define the meaning of each of
> the counters. For example, in ClassLoader.loadClass, it's not clear if
> you mean to include the time to check if the class has already been
> loaded (just on that one, if the lookup is not meant to be included
> then it would reduce the calls to nanoTimes a bit).
> Is it necessary to have separate counters for zip and JAR? If I'm
> reading this correctly, then zipFiles and jarFiles will both be
> incremented when a JAR file is opened - is that right?
> I agree with Rémi's comment that perf, name, and lb can be final.
> Would addElapsedTime(start) be better named as
> addElapsedTimeFrom(start) to make it clear that it doesn't add "start"
> to the elapsed time, but rather the elapsed time from the given
> starting time?
> This might sound crazy, but do the updates need to be synchronized? I
> don't think there is any synchronization in the VM. I agree with
> David's concern about the overhead of the calls to nanoTimes (which
> I'm sure you are measuring) but for the synchronization there are
> places where both a counter and an elapsed time are updated.
Classloading is now done in parallele, zip and jar can be loaded by
"for the synchronization there are places where both a counter and an
elapsed time are updated"
=> the problem is that these synchronisations are done on two different
I don't see how to remove them easily.
Furthermore I think that all synchronized can not be easily replaced by
some atomics operations
(unsafe.put* or unsafe.compareAndSwap) because long in a ByteBuffer
Perhaps with the Doug Lea's Fences (scheduled to be introduced in jdk7)
but I'm not sure.
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