RFR(M) 8150353: PPC64LE: Support RTM on linux

[Doerr, Martin]

Hi Vladimir,

thanks for taking a look.

About version values:
We are using a similar scheme for version checks on AIX where we know that the version values are less than 256.
It makes comparisons much more convenient.
But I agree that we should double-check if it is guaranteed for linux as well (and possibly add an assertion).

About scratch buffer size:
We only noticed that the scratch buffer was too small when we enable all RTM features:
-XX:+UnlockExperimentalVMOptions -XX:+UseRTMLocking -XX:+UseRTMForStackLocks -XX:+UseRTMDeopt
We have only tried on PPC64, but I wonder if the current size is sufficient for x86. I currently don't have access to a Skylake machine.

I think adding 1024 bytes to the scratch buffer doesn't hurt.
(It may also lead to larger CodeBuffers in output.cpp but I don't think this is problematic as long as the real content gets copied to nmethods.)
Would you agree?

Best regards,
Martin

-----Original Message-----
From: Vladimir Kozlov [mailto:vladimir.kozlov at oracle.com] 
Sent: Donnerstag, 25. Februar 2016 00:54
To: Gustavo Romero <gromero at linux.vnet.ibm.com>; Doerr, Martin <martin.doerr at sap.com>; hotspot-dev at openjdk.java.net
Cc: brenohl at br.ibm.com
Subject: Re: RFR(M) 8150353: PPC64LE: Support RTM on linux

My concern (but I am not export) is Linux version encoding. Is it true 
that each value in x.y.z is less then 256? Why not keep them as separate 
int values?
I also thought we have OS versions in make files but we check only gcc 
version there.

Do you have problem with ScratchBufferBlob only on PPC or on some other 
platforms too? May be we should make MAX_inst_size as platform specific 
value.

Thanks,
Vladimir

On 2/24/16 11:50 AM, Gustavo Romero wrote:
> Hi Martin,
>
> Both little and big endian Linux kernel contain the syscall change, so
> I did not include:
>
> #if defined(COMPILER2) && (defined(AIX) || defined(VM_LITTLE_ENDIAN)
>
> in globalDefinitions_ppc.hpp.
>
> Please, could you review the following change?
>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8150353
> Webrev (hotspot): http://81.de.7a9f.ip4.static.sl-reverse.com/webrev/
>
> Summary:
>
> * Enable RTM support for Linux on PPC64 (LE and BE).
> * Fix C2 compiler buffer size issue.
>
> Thank you.
>
> Regards,
> Gustavo
>