Increased safepoint cleanup tasks in Java 11 (vs 8)

[Vitaly Davidovich]

So after adding "cleanup" to ULF per Thomas' suggestion, I'm seeing the
following steps taking non-zero time:

   - deflating idle monitors
   - updating inline caches
   - compilation policy safepoint handler
   - purging class loader data graph
   - resizing system dictionaries

So I was wrong about this being string table rehashing.

https://github.com/openjdk/jdk11u/blob/737d8437886ad97c6ed21a25b9911c10b3886f61/src/hotspot/share/classfile/classLoaderData.hpp#L145
suggests
that CLDG purging is only done when using CMS.  This application isn't
using CMS (as mentioned, it's running ParallelGC).  It'd be nice if this
operation was entirely skipped and didn't show up in cleanup=info output.
I haven't (yet) checked if other cleanup ops (should?) have similar
"skipability".

But as Aleksey mentioned, it sounds like safepoint cleanup itself is now
additionally predicated on monitor deflation, and not just IC buffer
cleanup.  I'll test out his suggested (experimental) VM option.

On Wed, Jun 5, 2019 at 8:52 AM Vitaly Davidovich <vitalyd at gmail.com> wrote:

>
>
> On Wed, Jun 5, 2019 at 8:47 AM Thomas Schatzl <thomas.schatzl at oracle.com>
> wrote:
>
>> Hi,
>>
>> On Wed, 2019-06-05 at 08:33 -0400, Vitaly Davidovich wrote:
>> > Hi all,
>> >
>> [...]
>> >
>> > My guess would be it's SAFEPOINT_CLEANUP_STRING_TABLE_REHASH because
>> > tiered compilation is disabled, ParallelGC is being used, and biased
>> > locking is disabled; all of this is the same as on Java 8.  Or might
>> > this be something else? Presumably it's something "new" in Java 11
>> > that triggers inside
>> >
>>
>> https://github.com/openjdk/jdk11u/blob/737d8437886ad97c6ed21a25b9911c10b3886f61/src/hotspot/share/runtime/safepoint.cpp#L644
>> >
>> > Does anyone have ideas on pinpointing this further? How do I get the
>> > precise cleanup operation to show up in the log?
>>
>> Given above link, considering the "TraceTime timer(name,
>> TRACETIME_LOG(Info, safepoint, cleanup))" lines, I would try adding
>> safepoint+cleanup=info to your log options.
>>
> Ah, thanks Thomas! I "saw" the "cleanup" in there too, but didn't connect
> the dots that I had to also include that as a ULF tag (since already had
> "safepoint").  Makes sense.  I will try.
>
>>
>> Hth,
>>   Thomas
>>
>>
>>