Request for review (M): 7178361: G1: Make sure that PrintGC and PrintGCDetails use the same timing for the GC pause

[Bengt Rutisson]

Hi Vitaly,

Thanks for looking at this so quickly!

On 2012-06-20 15:59, Vitaly Davidovich wrote:
>
> Hi Bengt,
>
> Do you think it's worthwhile to add asserts to the double[] setters in 
> G1GCPhaseTimes to ensure that worker_i is within bounds? It may not 
> segfault but stomp memory instead if it's outside the bounds.  Maybe 
> overkill though ...
>

Good point I added the asserts.

I had been thinking of having extra checks for debug builds. We could 
check that all values for the active threads have been set before we try 
to use the values for anything. I think this might be overkill though, 
so I'm leaving that out for now.

> Also, should/can worker_i be uint? Or are negative values expected? Or 
> would this require casts from the caller because the rest of the 
> relevant code uses int?
>

Well, we use the worker_i value to directly index the arrays. A C++ 
array has to be indexed with a signed value.

Instead I added asserts that the worker_i values are >= 0. I also did 
(kind of the opposite of what you suggested) and made the instance 
variable _active_workers into an int instead of uint. This kind of make 
sense since we use int for the worker_i parameters. Otherwise I would 
have had to add casts in the new asserts.

I did one more minor change, so I'll send out updated webrevs in a minute.

Bengt

> Regards,
>
> VitalyVitaly
>
> Sent from my phone
>
> On Jun 20, 2012 9:14 AM, "Bengt Rutisson" <bengt.rutisson at oracle.com 
> <mailto:bengt.rutisson at oracle.com>> wrote:
>
>
>     Hi everyone,
>
>     Could I please have some reviews for this change:
>     http://cr.openjdk.java.net/~brutisso/7178361/webrev.00/
>     <http://cr.openjdk.java.net/%7Ebrutisso/7178361/webrev.00/>
>
>     Background
>     As part of the PrintGC and PrintGCDetails logging there is
>     information about how long the GC pause was. The timing of the
>     pause was done differently in G1 depending on whether PrintGC or
>     PrintGCDetails were enabled. It turns out that PrintGCDetails was
>     just timing part of the pause.
>
>     This change will make both PrintGC and PrintGCDetails use the same
>     timing. To achieve this I had to refactor the code a bit. I moved
>     all the timing data out of G1CollectorPolicy into a new class
>     called G1GCPhaseTimes.
>
>     My intention is that this change should not alter the format of
>     the output of PrintGC or PrintGCDetails. It should just correct
>     the timing data.
>
>     However, I did find that we are collecting timing information
>     about card counts, under an #ifdef. I moved this to the finest log
>     level instead. This does not change the existing format for normal
>     usage of PrintGC or PrintGCDetails.
>
>     Also, I had to update how the TraceGen0Time data is logged. I will
>     have another look at this, but my idea was to leave the format
>     exactly as it was. However, I think the format has decayed over
>     time so maybe I'll try to clean it up.
>
>     I intend to follow this change up with a change to remove the
>     special treatment of the single threaded case for PrintGCDetails
>     (tracked in CR 7178363).
>
>     Finally, this work revealed an issue with how the ergonomics in G1
>     measure the collection pauses. I did not want to change this
>     behavior now so I filed a separate RFE for that (7178365: G1:
>     Ergonomics only count part of the collection pause).
>
>     Bengt
>

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