[9] RFR(S): 8068945: Use RBP register as proper frame pointer in JIT compiled code on x86

Aleksey Shipilev aleksey.shipilev at oracle.com
Wed Apr 22 20:59:05 UTC 2015

On 03/31/2015 12:39 AM, Vladimir Kozlov wrote:
> Also the original request was to have flag to enable such behavior (use
> RBP only as FP). So to have it off by default is acceptable. If
> performance group or someone find a regression (or bug) due to this
> change we can switch the flag off by default before jdk9 release.

I'll save you a round-trip!

 a) there is a way enabling PreserveFramePointer can lead to performance
regression -- under high register pressure;
 b) there is an anecdotal evidence +PreserveFramePointer *does* lead to
performance regression (see Zoltan's fib benchmarks);
 c) frame pointer is required for a specific use case (stack walking by
native profilers), and Java profilers are able to walk through
Java-specific frames anyway (Forte/AsyncGetCallTrace).

...I would say this feature should be opt-in, not opt-out.

If you want it to be opt-out, then please work with someone from
performance team to establish if enabling this by default really is safe.


-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 819 bytes
Desc: OpenPGP digital signature
URL: <http://mail.openjdk.java.net/pipermail/hotspot-compiler-dev/attachments/20150422/c9de66a5/signature.asc>

More information about the hotspot-compiler-dev mailing list