RFR: 8143157: Convert TraceVMOperation to Unified Logging

[David Holmes]

Hi Rachel,

On 18/11/2015 5:50 AM, Rachel Protacio wrote:
> Hi,
>
> Please review the following small logging enhancement.
>
> Summary: The former -XX:+TraceVMOperation flag is updated to the unified
> logging framework and is now replaced with -Xlog:vmoperation in product
> mode.
>
> Open webrev: http://cr.openjdk.java.net/~rprotacio/8143157/
> Bug: https://bugs.openjdk.java.net/browse/JDK-8143157
> Testing: Passes jtreg, JPRT, RBT quick tests, and refworkload
> performance tests.

Meta-question: the logging framework is safe to be called when at a 
safepoint isn't it?

---

src/share/vm/runtime/vm_operations.cpp

   void VM_Operation::evaluate() {
     ResourceMark rm;
!   outputStream* debugstream = LogHandle(vmoperation)::debug_stream();
!   if (log_is_enabled(Debug, vmoperation)) {
!     debugstream->print("[");
!     print_on_error(debugstream);
!     debugstream->cr();
     }
     doit();
!   if (log_is_enabled(Debug, vmoperation)) {
!     print_on_error(debugstream);
!     debugstream->print_cr("]");
     }
   }

Why are you calling print_on_error twice?

Why is the only logging level for this tag the "debug" level? I think I 
may be missing part of the way UL works here - can you enable logging 
both by explicit tag (ie vmoperation) and the level (ie debug)?

And I know I sound like a broken record but I'm concerned about the 
overhead of the logging actions when it is not enabled ie:

outputStream* debugstream = LogHandle(vmoperation)::debug_stream();

always gets executed - and we evaluate is_enabled twice.

---

test/runtime/logging/VMOperationTestMain.java

Can you add a comment explaining what the logic is attempting to do 
please. I'm curious how many times the loop executes before you get a 
safepoint-based GC (and how it varies for different GC's).

Style nit: while(  -> while (

> A compatability request has been accepted with regard to this change.

I'll record my objections again to the conversion of develop flags to 
product. <sigh>

Thanks,
David

> Thank you very much,
> Rachel