[9] RFR(S): 8162881: Effect of -XX:CICompilerCount depends on ordering of other flags

[Tobias Hartmann]

Thanks, Vladimir!

Best regards,
Tobias

On 02.08.2016 23:46, Vladimir Kozlov wrote:
> Thank you for fixing this, Tobias
> 
> Changes looks good.
> 
> Thanks,
> Vladimir
> 
> On 8/2/16 5:30 AM, Tobias Hartmann wrote:
>> Hi,
>>
>> please review the following patch:
>> https://bugs.openjdk.java.net/browse/JDK-8162881
>> http://cr.openjdk.java.net/~thartmann/8162881/webrev.00/
>>
>> There are multiple problems and inconsistencies with the CICompilerCount flag:
>>
>> 1) We can not set the number of compiler threads to 1 if -TieredCompilation is specified after CICompilerCount=1:
>>   $ java -XX:CICompilerCount=1 -XX:-TieredCompilation -version
>>   CICompilerCount (1) must be at least 2
>>   Improperly specified VM option 'CICompilerCount=1'
>>   Error: Could not create the Java Virtual Machine.
>>   Error: A fatal exception has occurred. Program will exit.
>>
>> 2) We can not set the number of compiler threads to 1 if TieredStopAtLevel=1 is specified after CICompilerCount=1:
>>   $ java -XX:CICompilerCount=1 -XX:-TieredStopAtLevel=1 -XX:+PrintFlagsFinal -version
>>   CICompilerCount (1) must be at least 2
>>   Improperly specified VM option 'CICompilerCount=1'
>>   Error: Could not create the Java Virtual Machine.
>>   Error: A fatal exception has occurred. Program will exit.
>>
>> 3) The number of compiler counts can be set to 1 with TieredStopAtLevel=1 but has no effect:
>>   $ java -XX:TieredStopAtLevel=1 -XX:CICompilerCount=1 -XX:+PrintFlagsFinal -version | grep CICompilerCount
>>        intx CICompilerCount                          = 2                                        {product} {command line, ergonomic}
>>
>> 4) The value of CICompilerCount is listed as being "ergonomic" although it was set via command line:
>>   $ java -XX:TieredStopAtLevel=1 -XX:CICompilerCount=5 -XX:+PrintFlagsFinal -version | grep CICompilerCount
>>       intx CICompilerCount                          = 5                                        {product} {command line, ergonomic}
>>
>> To fix 1) and 2), I changed the ConstraintType of the CICompilerCount constraint to 'AfterErgo'. Like this, the value of CICompilerCount is only checked after the effect of -XX:-TieredCompilation took place.
>>
>> To fix 3), I added special cases to the initialization of SimpleThresholdPolicy and AdvancedThresholdPolicy to set the C2 compiler count to zero if TieredStopAtLevel < CompLevel_full_optimization.
>>
>> To fix 4), I changed the ergonomics code to only use FLAG_SET_ERGO if the value of CICompilerCount is updated. I also changed the computation of 'count' to always be >= 2 because with os::active_processor_count() == 1, count is ergonomically set to 1 but both c1_count and c2_count are set to 2. I added an assert to check for consistency.
>>
>> I added the corresponding test cases to CheckCICompilerCount.
>>
>> Tested with regression test, JPRT and RBT (running).
>>
>> Thanks,
>> Tobias
>>