[9] RFR(S): 8059606: Enable per-method usage of CompileThresholdScaling (per-method compilation thresholds)

[Zoltán Majó]

Hi,


please review the following patch.

Bug: https://bugs.openjdk.java.net/browse/JDK-8059606

Problem: Controlling compilation thresholds on a per-method level can be 
useful for debugging and understanding failures, but currently there is 
no way to control on a per-method level when methods are compiled.


Solution:

This patch adds support for scaling compilation thresholds on a 
per-method level using the CompileThresholdScaling flag. For example, 
the option

-XX:CompileCommand=option,SomeClass.someMethod,double,CompileThresholdScaling,0.5

reduces compilation thresholds for method SomeClass.sometMethod() by 50% 
(but leaves global thresholds unaffected) and results in earlier 
compilation of the method.

Similar to the global CompileThresholdScaling flag (added in 
JDK-805604), the per-method CompileThresholdScaling flag works with both 
tiered and non-tiered modes of operation.

Per-method compilation thresholds are available only in non-product 
builds to avoid the overhead of accessing fields added by the patch 
MethodData and MethodCounters.

The proposed patch supports x86_64, x86_32, and sparc. Do you think it 
is necessary to support other architectures as well?

The patch updates the name of the flags Tier2BackEdgeThreshold, 
Tier3BackEdgeThreshold, Tier4BackEdgeThreshold (lowercase e in 
"Back*e*dge) so that the naming is consistent with other 
backedge-related flags (Tier0BackedgeNotifyFreqLog, 
Tier2BackedgeNotifyFreqLog, and Tier3BackedgeNotifyFreqLog).

This patch is the third (and final) part of JDK-8050853: 
https://bugs.openjdk.java.net/browse/JDK-8050853 .


Webrev: http://cr.openjdk.java.net/~zmajo/8059606/webrev.00/

Testing: manual testing on all supported architectures, JPRT.

Thank you and best regards,


Zoltan