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

[Vladimir Kozlov]

Hi David,

Tiered is disabled because we don't want to see compilations and outputs 
from C1 compiler which does not have EA.

The test is specifically written for C2 only (not for C1 or Graal) to 
verify its Escape Analysis optimization.
I did not look in great details into test's code but its analysis may be 
affected if C1 compiler is also used.

Richard may clarify this.

thanks,
Vladimir

On 12/11/19 1:04 PM, David Holmes wrote:
On 12/12/2019 5:21 am, Vladimir Kozlov wrote:
I will do full review later. I want to comment about test command line.

You don't need vm.opt.TieredCompilation != true in @requires because 
you specified -XX:-TieredCompilation in @run command.

And per my comment this should be being tested with tiered as well.

David

Use vm.compMode == "Xmixed" instead of vm.compMode != "Xcomp" to skip 
test from running in Interpreter mode too.

Thanks,
Vladimir

On 12/11/19 7:07 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!

   > 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.hol...@oracle.com>
Sent: Mittwoch, 11. Dezember 2019 08:03
To: Reingruber, Richard <richard.reingru...@sap.com>; 
serviceability-dev@openjdk.java.net; 
hotspot-compiler-...@openjdk.java.net; 
hotspot-runtime-...@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