Hello again,
I have now regenerated the classlists @b107 and run new comparisons. To
me it looks like the differences are essentially non existant between
new and old classlists and in the previous comparison we saw no
difference between random order and old classlists.
It's very possible that it has an impact on cold starts, as Staffan
suggests, but we have no way (that I know of) of measuring that, and is
that really a valid requirement if we can't measure it?
/Erik
On 2013-08-20 03:54, David Holmes wrote:
Hi Erik,
Adding in hotspot-runtime-dev.
There is a lot of history here and I'm not sure who remembers all the
details - if anyone. There are existing open bugs to re-assess the
utility of the jarreorder (7032729) and to update the classlists
(8005688).
David
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On 20/08/2013 1:17 AM, Erik Joelsson wrote:
Hello,
I wonder if anyone knows more about the jarreorder tool and why we
use it?
As I understand it, we have precalculated classlists for each platform
(most likely outdated) and the tool is used to make sure those classes
end up in a specific order, last in rt.jar. I assume this is some kind
of startup time optimization.
I got some help from Claes in the performance team and did a quick run
of a startup and footprint benchmark, comparing a build with the rt.jar
reordered as normal and one where I simply turned off this feature and
let the files end up in the default order. Our preliminary findings show
that any difference between the two is negligible. Before we declare it
useless, we might need to test with freshly generated classlists? Does
anyone know how to generate them? Is there some other benefit of this
that I might have missed?
I would like to propose removing jarreorder to simplify the build. This
would also enable faster incremental builds of the images target, by not
having to rebuild the whole rt.jar every time.
/Erik
