How to change compilation policy to trigger C2 compilation ASAP?

[Vitaly Davidovich]

Thanks Kris.  Microsoft CLR also has something like that which they call
Multicore JIT (i.e. background compilations are started on separate cores
against saved profiles on startup).

I wonder if anything of the sort is on the roadmap for hotspot?

sent from my phone
On May 20, 2015 8:22 PM, "Krystal Mok" <rednaxelafx at gmail.com> wrote:

> ReadyNow does save profiles to disk and read them back in subsequent runs.
> There are also other changes on the side in the runtime and compilers to
> make it work smoothly.
>
> Cc'ing Doug Hawkins who's the one working on ReadyNow if anybody's
> interested in more information.
>
> - Kris
>
> On Wed, May 20, 2015 at 6:40 AM, Vitaly Davidovich <vitalyd at gmail.com>
> wrote:
>
>> Training mode is also dangerous unless built in from beginning as there's
>> risk some unwanted application effect will take place.  This is beside the
>> possibility of feeding it "wrong" profile.
>>
>> What does Azul ReadyNow do? Saves profiles to disk and reads them upon
>> startup?
>>
>> sent from my phone
>> On May 20, 2015 4:58 AM, "Chris Newland" <cnewland at chrisnewland.com>
>> wrote:
>>
>>> 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
>>> >>>>>>
>>> >>>>
>>> >>>
>>> >>
>>> >
>>> >
>>>
>>>
>>>
>
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