gc log analysis tools

Ben Cheng bccheng at google.com
Fri Oct 26 06:22:54 UTC 2007


On 10/25/07, Neo Jia <neojia at gmail.com> wrote:
>
> Ben,
>
> Which one should be better? lower score or higher score? I assume it
> should be higher based on what you said here.


Oops, I forgot to clarify that. Yes, the higher the better.

And, what is the relation between score and time? Will the execution
> time longer with a low score?



The benchmark is doing fixed workload, so the score is simply calculated as
work/s.

And how many minor GC and full GC in each of your execution? Just grep
> and wc them.



Almost all of them are minor GCs.

For 32-bit and 64-bit machine, at least the default heap layout is
> different. Are you trying to use same amount of nursery space and
> mature space.



I think I am just using the default ration. I only specify -Xmx and -Xms to
the same amount without using -Xmn.


> And for 64-bit machine, the Jitter is much more better than 32-bit
> machine, a lot of optimization is added.


I believe so, and that's why the 64-bit VM eventually provides 40% speedup
with larger heap is given. I think under the same amount of heap space there
are more GC activities in 64-bit VM due to larger object sizes. I will
grep/wc the total gc time then.

Thanks,
-Ben

So ...
>
> Thanks,
> Neo
>
> On 10/25/07, Ben Cheng <bccheng at google.com> wrote:
> > The reason I am interested in this information is because I have a
> benchmark
> > whose score is X using 32-bit VM and 2G of heap. When I switched to
> 64-bit
> > build of the same VM, the score dropped to 0.77X with the same amount of
> > heap. If I increase the heap size to 3.5G (on a machine with 4GB of
> RAM),
> > the score went to to 1.40X.
> >
> > What I need is pretty basic - it sums up all the gc time from the
> verbose
> > log during a benchmark run, as I want to verify if the change in gc time
> > correlates to the change in performance. I can write a similar script to
> do
> > that, but I just want to check to see if there is a working tool out
> there
> > already. Apparently the verbose gc log format changed from 1.5 and
> beyond
> > and the old script is not compatible.
> >
> > Thanks,
> > -Ben
> >
> >
> > On 10/25/07, Neo Jia <neojia at gmail.com> wrote:
> > > Ben,
> > >
> > > What is your opion? I had one but not sure if it would work for you or
> not
> > (
> > >
> > > I have not worked on JDK for a while ...
> > >
> > > Thanks,
> > > Neo
> > >
> > > On 10/25/07, Ben Cheng < bccheng at google.com> wrote:
> > > > Hi,
> > > >
> > > > I was trying to get a sense of total GC time spent in a Java app
> using
> > 1.6
> > > > JDK. The gc logs (w/ and wo/ parallel gc) seem to break the ancient
> tool
> > > > gc_analyze.pl found on the web.
> > > >
> > > > Is there an update to date tool to produce the desired information
> for
> > new
> > > > JDKs?
> > > >
> > > > Thanks in advance,
> > > > -Ben
> > > >
> > >
> > >
> > > --
> > > I would remember that if researchers were not ambitious
> > > probably today we haven't the technology we are using!
> > >
> >
> >
>
>
> --
> I would remember that if researchers were not ambitious
> probably today we haven't the technology we are using!
>
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