[12] RFR(S): 8177899: Tests fail due to code cache exhaustion on machines with many cores

[Tobias Hartmann]

Hi Martin,

thanks for the review!

Vladimir, are you okay with that version as well?

Best regards,
Tobias

On 29.10.18 14:32, Doerr, Martin wrote:
> Hi Tobias,
> 
> thanks for improving. Your update looks good.
> 
> Best regards,
> Martin
> 
> 
> -----Original Message-----
> From: Tobias Hartmann <tobias.hartmann at oracle.com> 
> Sent: Montag, 29. Oktober 2018 13:22
> To: Doerr, Martin <martin.doerr at sap.com>; Vladimir Kozlov <vladimir.kozlov at oracle.com>; hotspot-compiler-dev at openjdk.java.net
> Subject: Re: [12] RFR(S): 8177899: Tests fail due to code cache exhaustion on machines with many cores
> 
> Hi Martin,
> 
> On 26.10.18 16:21, Doerr, Martin wrote:
>>> Well it's just an upper limit and the number of compiler threads that are actually created should be
>>> controlled by -XX:+UseDynamicNumberOfCompilerThreads.
>> I know, but it looks like a complicated computation for a simple task which is difficult to maintain if the other code changes.
>> As you have written, it can happen that the threads really get started and I don't see any benefit of starting so many threads that most of them can never generate a nmethod because it simply wouldn't fit.
>> Anyway, your change seems to fix the issue and if other reviewers like it this way, ok.
> 
> Yes I just think that since the available space in the code cache is a dynamic property, it should
> also be used in a dynamic way to bound the number of compiler threads. I.e, ReservedCodeCacheSize
> should serve as an upper bound for CICompilerCound and the actual available space should be part of
> the UseDynamicNumberOfCompilerThreads heuristic.
> 
>>> I think the heuristic should be improved to
>>> consider the available space in the code cache as well (not only the available memory). Since the
>>> available space in the code cache depends on many factors, I don't think a constant is feasible. I
>>> would prefer to file a RFE for that.
>> That sounds like a good idea, too.
> 
> I've filed JDK-8213086 [1]. Feel free to take it, I probably won't have time to work on it soon.
> 
>>> While looking at the computation again, I've noticed that JDK-8209594 increased the buffer size.
>>> I've updated C2Compiler::initial_code_buffer_size() accordingly:
>>> http://cr.openjdk.java.net/~thartmann/8177899/webrev.02/
>> Thanks for updating. Looks correct. I think this function could be used in compile.cpp, now to avoid code duplication.
> 
> Right, I've used the corresponding function both in c1_Compiler.cpp and c2compiler.cpp:
> http://cr.openjdk.java.net/~thartmann/8177899/webrev.03/
> 
> Thanks,
> Tobias
> 
> [1] https://bugs.openjdk.java.net/browse/JDK-8213086
>