How to change compilation policy to trigger C2 compilation ASAP?

[Chris Newland]

Hi Wei,

Is there any reason why you need to cold-start your application each time
and begin with no profiling information?

Depending on your input data, would it be possible to "warm up" the VM by
running typical inputs through your code to build a rich profile and have
the JIT compilations performed before your real data arrives?

One reason *against* doing this would be wide variations in your input
data that could result in the wrong optimisations being made and possibly
suffering a decompilation event.

There are commercial VMs that have technology to mitigate cold-start costs
(for example Azul Zing's ReadyNow).

Have you examined the HotSpot LogCompilation output to make sure there is
nothing you could change at source code level which would result in a
better JIT decisions? I'm thinking of things like inlining failures due to
call-site megamorphism.

There's a free tool called JITWatch that aims to make it easier to
understand the LogCompilation output
(https://github.com/AdoptOpenJDK/jitwatch) (Sorry for the sales pitch -
I'm the author).

Regards,

Chris
@chriswhocodes

On Wed, May 20, 2015 03:11, Vitaly Davidovich wrote:
> I'll let Vladimir comment on the compile command, but turning off tiered
> doesn't prevent inlining.  What prevents inlining (an otherwise inlineable
>  method), in a nutshell, is lack of profiling information that would
> indicate the method or callsite is hot enough for inlining.  So you can
> have tiered off and run C2 with standard compilation thresholds, and
> you'll likely get good inlining because you'll have a long profile.  If
> you turn C2 compile threshold down too far (and too far is going to be
> app-specific), C2 compilation may not have sufficient info in the
> shortened profile to decide to inline.  Or even worse, the profile
> collected is actually not reflective of the real profile you want to
> capture (e.g. app has a phase change after initialization).
>
> The theoretical advantage of tiered is you can get decent perf quickly,
> but also since you're getting better than interpreter speed quickly, you
> can run in C1 tier longer and thus collect an even larger profile,
> possibly leading to better code than C2 alone.  But unfortunately this may
> require serious tuning.  That's my understanding at least.
>
> sent from my phone On May 19, 2015 10:00 PM, "Tangwei (Euler)"
> <tangwei6 at huawei.com> wrote:
>
>
>> Vladimir,
>> What the 'double' means in following command line? The option
>> CompileThresholdScaling you mentioned is same as
>> ProfileMaturityPercentage?
>> I cannot find the option in code. How much effect to function inlining
>> by turning off tiered compilation?
>>
>>>
>> -XX:CompileCommand=option,SomeClass.someMethod,double,CompileThresholdS
>> caling,0.5
>>
>> Regards!
>> wei
>>
>>> -----Original Message-----
>>> From: Vladimir Kozlov [mailto:vladimir.kozlov at oracle.com]
>>> Sent: Wednesday, May 20, 2015 9:12 AM
>>> To: Tangwei (Euler); Vitaly Davidovich
>>> Cc: hotspot compiler
>>> Subject: Re: How to change compilation policy to trigger C2
>>> compilation
>> ASAP?
>>
>>>
>>> If you want only C2 compilation you can disable tiered compilation
>>>
>> (since you
>>
>>> don't want to spend to much on profiling anyway) and set low
>>> CompileThreshold (you need only this one for non-tiered compile):
>>>
>>>
>>> -XX:-TieredCompilation -XX:CompileThreshold=100
>>>
>>>
>>> If your method is simple and don't need profiling or inlining the
>>>
>> generated code
>>> could be same quality as with long profiling.
>>>
>>> An other approach is to set threshold per method (scale all
>>> threasholds
>> (C1, C2,
>>
>>> interpreter) by this value). For example to reduce thresholds by
>>> half:
>>>
>>>
>>> -XX:CompileCommand=option,SomeClass.someMethod,double,CompileThresh
>>> oldScaling,0.5
>>>
>>> Vladimir
>>>
>>>
>>> On 5/19/15 5:43 PM, Tangwei (Euler) wrote:
>>>
>>>> My goal is just to reach peak performance quickly. Following is one
>>>>  tier threshold combination I tried:
>>>>
>>>> -XX:Tier0ProfilingStartPercentage=0
>>>>
>>>>
>>>> -XX:Tier3InvocationThreshold=3
>>>>
>>>>
>>>> -XX:Tier3MinInvocationThreshold=2
>>>>
>>>>
>>>> -XX:Tier3CompileThreshold=2
>>>>
>>>>
>>>> -XX:Tier4InvocationThreshold=4
>>>>
>>>>
>>>> -XX:Tier4MinInvocationThreshold=3
>>>>
>>>>
>>>> -XX:Tier4CompileThreshold=2
>>>>
>>>>
>>>> Regards!
>>>>
>>>>
>>>> wei
>>>>
>>>> *From:*Vitaly Davidovich [mailto:vitalyd at gmail.com]
>>>> *Sent:* Tuesday, May 19, 2015 9:33 PM
>>>> *To:* Tangwei (Euler)
>>>> *Cc:* hotspot compiler
>>>> *Subject:* Re: How to change compilation policy to trigger C2
>>>> compilation ASAP?
>>>>
>>>> Is your goal specifically to have C2 compile or just to reach peak
>>>> performance quickly? It sounds like the latter.  What values did you
>>>>  specify for the tier thresholds? Also, it may help you to
>>>> -XX:+PrintCompilation to tune the flags as this will show you which
>>>>  methods are being compiled, when, and at what tier.
>>>>
>>>> sent from my phone
>>>>
>>>> On May 19, 2015 9:01 AM, "Tangwei (Euler)" <tangwei6 at huawei.com
>>>> <mailto:tangwei6 at huawei.com>> wrote:
>>>>
>>>>
>>>> Hi All,
>>>>
>>>>
>>>> I want to run a JAVA application on a performance simulator, and do
>>>>  a profiling on a hot function JITTed with C2 compiler.
>>>>
>>>> In order to make C2 compiler compile hot function as early as
>>>> possible, I hope to reduce the threshold of function invocation
>>>>
>>>> count in interpreter and C1 to drive the JIT compiler transitioned
>>>> to Level 4 (C2) ASAP. Following is the option list I try, but
>>>>
>>>>
>>>> failed to find a right combination to meet my requirement. Anyone
>>>> can help to figure out what options I can use?
>>>>
>>>> Thanks in advance.
>>>>
>>>>
>>>> -XX:Tier0ProfilingStartPercentage=0
>>>>
>>>>
>>>> -XX:Tier3InvocationThreshold
>>>>
>>>>
>>>> -XX:Tier3MinInvocationThreshold
>>>>
>>>>
>>>> -XX:Tier3CompileThreshold
>>>>
>>>>
>>>> -XX:Tier4InvocationThreshold
>>>>
>>>>
>>>> -XX:CompileThreshold
>>>>
>>>>
>>>> -XX:Tier4MinInvocationThreshold
>>>>
>>>>
>>>> -XX:Tier4CompileThreshold
>>>>
>>>>
>>>> Regards!
>>>>
>>>>
>>>> wei
>>>>
>>
>