RFR(L) 8227745: Enable Escape Analysis for Better Performance in the Presence of JVMTI Agents

[David Holmes]

On 12/12/2019 1:07 am, Reingruber, Richard wrote:
> Hi David,
> 
>    > Most of the details here are in areas I can comment on in detail, but I
>    > did take an initial general look at things.
> 
> Thanks for taking the time!

Apologies the above should read:

"Most of the details here are in areas I *can't* comment on in detail ..."

David

>    > The only thing that jumped out at me is that I think the
>    > DeoptimizeObjectsALotThread should be a hidden thread.
>    >
>    > +  bool is_hidden_from_external_view() const { return true; }
> 
> Yes, it should. Will add the method like above.
> 
>    > Also I don't see any testing of the DeoptimizeObjectsALotThread. Without
>    > active testing this will just bit-rot.
> 
> DeoptimizeObjectsALot is meant for stress testing with a larger workload. I will add a minimal test
> to keep it fresh.
> 
>    > Also on the tests I don't understand your @requires clause:
>    >
>    >   @requires ((vm.compMode != "Xcomp") & vm.compiler2.enabled &
>    > (vm.opt.TieredCompilation != true))
>    >
>    > This seems to require that TieredCompilation is disabled, but tiered is
>    > our normal mode of operation. ??
>    >
> 
> I removed the clause. I guess I wanted to target the tests towards the code they are supposed to
> test, and it's easier to analyze failures w/o tiered compilation and with just one compiler thread.
> 
> Additionally I will make use of compiler.whitebox.CompilerWhiteBoxTest.THRESHOLD in the tests.
> 
> Thanks,
> Richard.
> 
> -----Original Message-----
> From: David Holmes <david.holmes at oracle.com>
> Sent: Mittwoch, 11. Dezember 2019 08:03
> To: Reingruber, Richard <richard.reingruber at sap.com>; serviceability-dev at openjdk.java.net; hotspot-compiler-dev at openjdk.java.net; hotspot-runtime-dev at openjdk.java.net
> Subject: Re: RFR(L) 8227745: Enable Escape Analysis for Better Performance in the Presence of JVMTI Agents
> 
> Hi Richard,
> 
> On 11/12/2019 7:45 am, Reingruber, Richard wrote:
>> Hi,
>>
>> I would like to get reviews please for
>>
>> http://cr.openjdk.java.net/~rrich/webrevs/2019/8227745/webrev.3/
>>
>> Corresponding RFE:
>> https://bugs.openjdk.java.net/browse/JDK-8227745
>>
>> Fixes also https://bugs.openjdk.java.net/browse/JDK-8233915
>> And potentially https://bugs.openjdk.java.net/browse/JDK-8214584 [1]
>>
>> Vladimir Kozlov kindly put webrev.3 through tier1-8 testing without issues (thanks!). In addition the
>> change is being tested at SAP since I posted the first RFR some months ago.
>>
>> The intention of this enhancement is to benefit performance wise from escape analysis even if JVMTI
>> agents request capabilities that allow them to access local variable values. E.g. if you start-up
>> with -agentlib:jdwp=transport=dt_socket,server=y,suspend=n, then escape analysis is disabled right
>> from the beginning, well before a debugger attaches -- if ever one should do so. With the
>> enhancement, escape analysis will remain enabled until and after a debugger attaches. EA based
>> optimizations are reverted just before an agent acquires the reference to an object. In the JBS item
>> you'll find more details.
> 
> Most of the details here are in areas I can comment on in detail, but I
> did take an initial general look at things.
> 
> The only thing that jumped out at me is that I think the
> DeoptimizeObjectsALotThread should be a hidden thread.
> 
> +  bool is_hidden_from_external_view() const { return true; }
> 
> Also I don't see any testing of the DeoptimizeObjectsALotThread. Without
> active testing this will just bit-rot.
> 
> Also on the tests I don't understand your @requires clause:
> 
>    @requires ((vm.compMode != "Xcomp") & vm.compiler2.enabled &
> (vm.opt.TieredCompilation != true))
> 
> This seems to require that TieredCompilation is disabled, but tiered is
> our normal mode of operation. ??
> 
> Thanks,
> David
> 
>> Thanks,
>> Richard.
>>
>> [1] Experimental fix for JDK-8214584 based on JDK-8227745
>>       http://cr.openjdk.java.net/~rrich/webrevs/2019/8214584/experiment_v1.patch
>>