[13] RFR(L) 8220623: [JVMCI] Update JVMCI to support JVMCI based Compiler compiled into shared library

[Vladimir Kozlov]

On 4/2/19 4:51 PM, Kim Barrett wrote:
>> On Apr 2, 2019, at 4:41 PM, Vladimir Kozlov <vladimir.kozlov at oracle.com> wrote:
>>
>> I ran Kitchensink with G1 and -Xmx8g. I observed that Remark pause times are not consistent even without Graal.
>> To see effect I added time spent in JVMCI::do_unloading() to GC log (see below [3]). The result is < 1ms - it is less than 1% of a pause time.
>>
>> It will have even less effect since I moved JVMCI::do_unloading() from serial path to parallel worker thread as Stefan suggested.
> 
> A few comments, while I'm still looking at this.
> 
> ------------------------------------------------------------------------------
> src/hotspot/share/gc/shared/parallelCleaning.cpp
>   213     JVMCI_ONLY(_jvmci_cleaning_task.work(_unloading_occurred);)
> 
> I think putting the serial JVMCI cleaning task at the end of the
> ParallelCleaningTask can result in it being mostly run by itself,
> without any parallelism. I think it should be put up front, so the
> first thread in starts working on it right away, while later threads
> can pick up other work.

Should we really put it to the beginning? It takes < 1ms.
May be other tasks are more expensive and should be run first as now.
But I don't know what is strategy is used here: run short or long tasks first.
If you think it is okay to move it - I will move it.

> 
> That's assuming this is all needed. I see that the Java side of things
> is using WeakReference to do cleanup. I haven't figured out yet why
> this new kind of weak reference mechanism in the VM is required in
> addition to the Java WeakReference cleanup.  Still working on that...
> 
> ------------------------------------------------------------------------------
> src/hotspot/share/gc/shared/parallelCleaning.cpp
>   194 #if INCLUDE_JVMCI
>   195   _jvmci_cleaning_task(is_alive),
>   196 #endif
> 
> This could be made a bit less cluttered:
> 
>    JVMCI_ONLY(_jvmci_cleaning_task(is_alive) COMMA)

Yes, I will do this. I tried use JVMCI_ONLY with regular ',' and it failed.

Thanks,
Vladimir

> 
> ------------------------------------------------------------------------------
> src/hotspot/share/runtime/jniHandles.cpp
>   192 #if INCLUDE_JVMCI
>   193   JVMCI::oops_do(f);
>   194 #endif
> 
> I don't think that belongs here.
> 
> ------------------------------------------------------------------------------
>