[9] RFR(S): 8059604: Add CompileThresholdScalingPercentage flag to control when methods are first compiled (with +/-TieredCompilation)

[Zoltán Majó]

Hi,


please review the following patch.


Bug: https://bugs.openjdk.java.net/browse/JDK-8059604


Problem: With tiered compilation enabled, the value of 6 different 
thresholds must be set to control when the JVM compiles methods for the 
first time. That is too detailed for the average customer.


Solution: This patch adds a new flag, CompileThresholdScalingPercentage, 
to control when methods are first compiled. The new flag scales 
thresholds the following way:

- if CompileThresholdScalingPercentage==100, the default threshold 
values are used
- if CompileThresholdScalingPercentage>100, threshold values are scaled 
up (e.g., CompileThresholdScalingPercentage=120 scales up thresholds by 
a factor of 1.2X)
- if 0 < CompileThresholdScalingPercentage < 100, threshold values are 
scaled down accordingly.

The new flag works both with and without tiered compilation. Thus, the 
new flag allows compilation to be controlled the same way both with and 
without tiered compilation:

- with tiered compilation enabled, the value of the flags 
Tier0InvokeNotifyFreqLog, Tier0BackedgeNotifyFreqLog, 
Tier3InvocationThreshold, Tier3MinInvocationThreshold, 
Tier3CompileThreshold, and Tier3BackEdgeThreshold is scaled

- with tiered compilation disabled, the value of CompileThreshold is scaled

Currently, tiered and non-tiered compilation treats threshold values 
slightly differently: For a threshold value of N and without tiered 
compilation enabled, methods are compiled *before* their Nth execution. 
With tiered compilation enabled, methods are compiled *after* the their 
Nth execution.

The patch addresses the difference between tiered/non-tiered 
compilation: Methods are compiled right before their Nth execution in 
both cases (the non-tiered way). If 
CompileThresholdScalingPercentage==0, all methods are interpreted 
(similarly to the case when CompileThreshold==0).

This patch is the second (out of three) parts of JDK-8050853 (adding 
support for per-compilation thresholds): 
https://bugs.openjdk.java.net/browse/JDK-8050853 .


Webrev: http://cr.openjdk.java.net/~zmajo/8059604/webrev.00/


Testing: JPRT, manual testing


Thank you and best regards,


Zoltan