question about PrintOptoStatistics atomicity

[Liu, Xin]

Hi, Vladimir, 

Thank you for you information. 
I understand. I can use -XX:CICompilerCount=2 if I need to have precise counters. 

thanks,
--lx


________________________________________
From: hotspot-compiler-dev <hotspot-compiler-dev-retn at openjdk.java.net> on behalf of Vladimir Kozlov <vladimir.kozlov at oracle.com>
Sent: Wednesday, July 15, 2020 10:50 AM
To: hotspot-compiler-dev at openjdk.java.net
Subject: RE: [EXTERNAL] question about PrintOptoStatistics atomicity

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It was done intentionally because when that code was implemented atomic operations were expensive.
We never intended these counters to be precise - they were used mostly for debugging purpose.
It is up to user how he want to use them - for example using only one C2 thread.
When you collect data for general application you want to execute it with the same parameters as in production. I don't
think we should enforce any restrictions in VM when PrintOptoStatistics is used.

Regards,
Vladimir K

On 7/15/20 8:31 AM, Liu, Xin wrote:
> Hi,
>
>
> I have a question about -XX:+PrintOptoStatistics in c2_globals.hpp.
>
> It dumps many internal counters in different C2 phases.  I found those counters are all static fields.
>
> eg.
>
> http://hg.openjdk.java.net/jdk/jdk/file/4b9ced2b948c/src/hotspot/share/opto/chaitin.cpp#l2297
>
> http://hg.openjdk.java.net/jdk/jdk/file/4b9ced2b948c/src/hotspot/share/opto/phaseX.hpp#l599
>
>
> I notice that all setters of those fields are not atomic. IMHO, hotspot may has more than one c2-compiler-threads running at the same time.
>
> How does hotspot guarantee those fields are thread-safe? or the flag intends to do statistics in single-thread mode by design?
>
>
> If those counters are not atomic, shall we connect this flag to CICompilerCount?
>
> I think we can constrain the number of c2-compiler-thread to 1 if user set PrintOptoStatistics. Does it make sense?
>
>
> thanks,
>
> --lx
>