PrintGCApplicationConcurrentTime / PrintGCApplicationStoppedTime

[Jon Masamitsu]

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.
> 
>