[9] RFR (XS): 8157560: Reserve space for allocation prefetch only in builds that support allocation prefetching

[Tobias Hartmann]

Hi Zoltan,

On 23.05.2016 13:00, Zoltán Majó wrote:
> Hi,
> 
> 
> please review the path for 8157560.
> 
> https://bugs.openjdk.java.net/browse/JDK-8157560
> 
> Problem: Every thread-local allocation buffer (TLAB) contains a reserved area to accommodate allocation prefetches (i.e., to make sure that instructions performing allocation prefetch do not cause faults). The reserved area is at the end of the TLAB.
> 
> Currently, all the reserved area is created in all builds, even though only the C2 compiler generates allocation prefetches. As a result, in builds without C2, some heap space is wasted at the end of each TLAB. Creating the reserved area also causes problems for internal testing of the AllocatePrefetchLines/AllocateInstancePrefetchLines command-line flags.
> 
> Solution: Create the reserved area only in C2-enabled builds. Re-enable testing of the AllocatePrefetchLines/AllocateInstancePrefetchLines flags.

This looks good to me!

Best regards,
Tobias

> 
> Webrev:
> http://cr.openjdk.java.net/~zmajo/8157560/webrev.00/
> 
> Testing:
> - JPRT;
> - pre-PIT RBT in progress;
> - internal tests -- all pass.
> 
> I plan to push the fix directly into hs as testing of AllocatePrefetchLines/AllocateInstancePrefetchLines is disabled only in hs.
> 
> Thank you!
> 
> Best regards,
> 
> 
> Zoltan
>