RFR (S): 8067014: LinearScan::is_sorted significantly slows down fastdebug builds' performance

[Aleksey Shipilev]

Hi Filipp,

On 02/12/2016 02:47 PM, Filipp Zhinkin wrote:
> here is a new webrev: http://cr.openjdk.java.net/~fzhinkin/8067014/webrev.01/

The webrev seems incomplete: it has only hotspot.patch in it, but no
other views?

I wonder how many intervals have the same "from", prompting you to
wiggle around looking for the exact interval? Can we define
"interval_cmp" so that "(interval_cmp(i1, i2) == 0) iff (i1 == i2)", or
at least make the false positives less frequent with more extensive
interval key (assuming collisions are indeed problematic)?


> I've hacked VM sources a bit to run CTW with product bits and C1
> compilation time on my x86_64 linux laptop
> slowed down by 0.4% (from 51029 ± 306 ms to 51230 ± 293 ms). Please
> let me know if it too slow.

I think this is within the error margin, and therefore statistically
insignificant. Even if it was significant, 0.4% is okay for compilation
time regression in C1.

> With fastdebug bits provided patch allow to reduce C1 compilation time twice.

This is a very good improvement, but we need to see if that's the end of
it, or we can squeeze even more with a few changes. I would suggest
running the CTW scenario under Solaris Studio Performance Analyzer (see
e.g.
http://shipilev.net/blog/2016/arrays-wisdom-ancients/#_meet_solaris_studio_performance_analyzer).

Thanks,
-Aleksey


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