How to change compilation policy to trigger C2 compilation ASAP?

[Chris Newland]

Hi Wei,

Thanks! OpenJDK has no support for persisting compilation profile data
between VM runs. For some industries it can be economical to use a
commercial VM to get the lowest latencies.

One "free" alternative is to add a training mode to your application and
feed it the most realistic input data so that you get a good set of JIT
optimisations before the inputs you care about arrive.

Is there a reason why you are cold-starting your VM? (For example your GC
strategy is to use a huge Eden space and reboot daily to avoid any garbage
collections).

Regards,

Chris
@chriswhocodes

On Wed, May 20, 2015 09:17, Tangwei (Euler) wrote:
> Hi Chris,
> Your tool looks cool. I think OpenJDK has no technology to mitigate
> cold-start costs, please correct if I am wrong. I can control some
> compilation passes with option -XX:CompileCommand, but the profiling
> data, such as invocation count and backedge count, has to reach some
> threshold before trigger execution level transition. This causes
> simulator doesn't trigger C2 compilation within reasonable time span.
>
> Regards!
> wei
>
>> -----Original Message-----
>> From: Chris Newland [mailto:cnewland at chrisnewland.com]
>> Sent: Wednesday, May 20, 2015 3:46 PM
>> To: Vitaly Davidovich
>> Cc: Tangwei (Euler); Vladimir Kozlov; hotspot compiler
>> Subject: RE: How to change compilation policy to trigger C2 compilation
>> ASAP?
>>
>>
>> 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,CompileThresh
>> ol
>>>> dS 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
>>>>>>
>>>>
>>>
>>
>
>