PrintGCApplicationConcurrentTime / PrintGCApplicationStoppedTime

Jon Masamitsu Jon.Masamitsu at Sun.COM
Thu Apr 16 06:48:29 PDT 2009


Sentiment at this point seems to favor including
the application times (stopped time and run time)
for all the safepoints.  We'll start on making that
the fix.

On 04/14/09 11:14, Jon Masamitsu wrote:
> Question: Do users care about applications times output
> for PrintGCApplicationConcurrentTime only relative to
> GC's?
> 
> 
> I have a CR
> 
> 6782663: Data produced by PrintGCApplicationConcurrentTime and 
> PrintGCApplicationStoppedTime is not accurate
> 
> where the complaint is that the application time as output
> for PrintGCApplicationConcurrentTime does not match the time
> as measured by the time between GC timestamps.  Actually the
> user is adding up all the times reported for
> PrintGCApplicationConcurrentTime between the GC timestamps
> and saying that that sum can be vastly off from the
> time between GC timestamps.  And the user is right.
> 
> I think the problem is that the timers used to report
> PrintGCApplicationConcurrentTime are updated more often
> than the PrintGCApplicationConcurrentTime time is
> reported.  In VMThread::loop() in share/vm/runtime/vmThread.cpp
> around line 425 the PrintGCApplicationConcurrentTime is
> reported before the call to SafepointSynchronize::begin().
> Whereas near line 391 and near line 520 calls to
> SafepointSynchronize::begin() do not report for
> PrintGCApplicationConcurrentTime.  The calls to
> SafepointSynchronize::begin() will update the application
> timer (_app_timer via a call to
> RuntimeService::record_safepoint_begin()).  Updating
> resets the timer to the current time and the
> PrintGCApplicationConcurrentTime output is then the
> time since the last safepoint (not since the application
> restarted after the last GC).
> 
> So anyone know why the PrintGCApplicationConcurrentTime output
> does not print for all safepoints?  Should it only printout
> when a VM operation is executed as it does now?
> 
> If yes, should the spelling of
> PrintGCApplicationConcurrentTime be changed to drop
> the GC, PrintApplicationConcurrentTime.  Similarly with
> PrintGCApplicationStoppedTime -> PrintApplicationStoppedTime.
> 
> Or should it printout for all safepoints?  This is
> simpler in that the printing could be added to
> RuntimeService::record_safepoint_begin()) so
> we would not miss new safepoints.  But we might
> be dumping useless information.
> 
> Or I could hack the code so that information is only
> printed around GC's.  And maybe not printout some
> useful information.
> 
> 



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