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

[Albert Noll]

Hi Zoltan,

here is some high-level feedback:

How about using a scaling factor instead of using percentage?
What happens if a threshold becomes 0 after scaling?

Best,
Albert


On 10/07/2014 12:32 PM, Zoltán Majó wrote:
> 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
>