RFR: 8274910: Compile in G1 evacuation failure injection code based on define

[Albert Mingkun Yang]

On Thu, 7 Oct 2021 14:25:04 GMT, Thomas Schatzl <tschatzl at openjdk.org> wrote:

> Hi all,
> 
>   can I have reviews for this change that simplifies performance work with evacuation failure handling a little? In particular, it adds a define called `EVAC_FAILURE_INJECTOR` (on by default in non-product builds) that allows to compile in/out the relevant injector code also in product mode (if manually enabled).
> 
> Actually, this PR suggests two variants for this: one that also automatically enables flags when `EVAC_FAILURE_INJECTOR` is selected (beaa6c3), and one that requires the developer also change the options from develop/notproduct to product to be available (9f07ffd).
> 
> The first is maybe makes the change a bit too hacky in `g1_globals.hpp` (unless there are ways to do that better, i.e. I could move the `GC_G1_EVACUATION_FAILURE_FLAGS` somewhere, or there is a much better preprocessor trick here, so I would like to have you decide.
> 
> Testing: gha, manual checking that in product mode by default no evacuation failure handling is in, but with the flag, and otherwise the same as before, tier1-5
> 
> Thanks,
>   Thomas

Marked as reviewed by ayang (Reviewer).

src/hotspot/share/gc/g1/g1_globals.hpp line 36:

> 34: #elif !defined(EVAC_FAILURE_INJECTOR)
> 35: #define EVAC_FAILURE_INJECTOR 0
> 36: #endif

Since the intended use case to include evac-fail code in a release build for perf evalucation, instead of accepting an already-defined `EVAC_FAILURE_INJECTOR`, one can bluntly reject it to make the intention more explicitly: this `#define` is the authoritative source of  `EVAC_FAILURE_INJECTOR`. Sth along the lines of:


#ifdef EVAC_FAILURE_INJECTOR
#error "EVAC_FAILURE_INJECTOR defined"
#endif
#ifdef PRODUCT
...

When the need to cope with externally defined `EVAC_FAILURE_INJECTOR` arises (I doubt it), we can revisit this at that time.

Ofc, this is quite subjective.

-------------

PR: https://git.openjdk.java.net/jdk/pull/5851