Remi,
Why do you need getHistoricInt ?
Is it because Unsafe.getInt() doesn't do any constant folding ?
Exactly. I need a compile-time constant to feed it to the compiler to
guide compilation.
BTW, why getHistoricInt is named getHistoricInt ?
From application perspective, the call returns current or some of the
previous values a field has.
Best regards,
Vladimir Ivanov
cheers,
Rémi
On 10/10/2014 09:08 PM, Vladimir Ivanov wrote:
http://cr.openjdk.java.net/~vlivanov/8059877/webrev.00/
https://bugs.openjdk.java.net/browse/JDK-8059877
LambdaForm sharing introduces profile pollution in compiled
LambdaForms. The most serious consequence is inlining distortion,
which severely degrade peak performance. The main victim is
guardWithTest (GWT) combinator.
Before LambdaForm sharing, inlining in GWT was affected by 2 aspects:
- branch frequencies: never-taken branch is skipped;
- target & fallback method handles (corresponding LFs: compiled vs
interpreted): if method handle has been invoked < COMPILE_THRESHOLD
times, LambdaForm.vmentry points to LF interpreter which is marked w/
@DontInline.
LambdaForm sharing breaks both aspects:
- sharing of GWT LambdaForm pollutes branch profile;
- sharing of LambdaForms used in target & fallback pollutes
invocation counters.
I experimented w/ VM API to guide JIT-compiler using profiling
information gathered on LambdaForm level [1], but decided to take
safer route for now (8u40). JIT-compiler control approach looks
promising, but I need more time to get rid of some performance
artifacts it suffers from.
The proposed fix is to mimic behavior of fully customized LambdaForms.
When GWT is created, both target & fallback method handles are wrapped
in a special reinoker, which blocks inlining (@DontInline on
reinvoker's compiled LambdaForm). Once a wrapper is invoked more that
DONT_INLINE_THRESHOLD times, it's LambdaForm is replaced with a
regular reinvoker, which is fully transparent for the JIT and it
inlines smoothly.
The downside of the chosen approach is that LambdaForm.updateForm()
doesn't guarantee that all places where stale LambaForm is used see
the update. If it is already part of some nmethod, it won't be
invalidated and recompiled, but will be kept as is. It shouldn't be a
problem, since DONT_INLINE_THRESHOLD is expected to be pretty low
(~30), so only very rarely executed branches are affected.
The fix significantly improves peak performance w/ full LF sharing
(USE_LF_EDITOR=true).
Octane/nashorn results [2] for:
(1) USE_LF_EDITOR=false DONT_INLINE_THRESHOLD=0 (default for 8u40&9)
(2) USE_LF_EDITOR=true DONT_INLINE_THRESHOLD=0 (default for 8u40&9)
(3) USE_LF_EDITOR=true DONT_INLINE_THRESHOLD=30 (fixed version)
(1) & (2) correspond to default configurations (partial & full LF
sharing respectively). (3) is the fixed version.
The fix recovers peak performance for:
* Crypto: ~255ms -> ~12ms;
* DeltaBlue: ~40ms -> ~2ms;
* Raytracer: ~62ms -> ~7ms;
* EarleyBoyer: ~160ms -> ~22ms;
* NavierStokes: ~17ms -> ~13ms;
2 subbenchmarks (Box2D & Gbemu) still has some regressions, but it's
much better now:
Box2D: ~48ms -> ~61ms (w/o the fix: ~155ms)
Gbemu: ~88ms -> ~116ms (w/o the fix: ~160ms)
Testing:
tests: jck (api/java_lang/invoke), jdk/java/lang/invoke,
jdk/java/util/streams, octane
configurations: -ea -esa -Xverify:all
+ COMPILE_THRESHOLD={0,30} + USE_LF_EDITOR={false,true} +
DONT_INLINE_THRESHOLD={0,30}
Thanks!
Best regards,
Vladimir Ivanov
[1] http://cr.openjdk.java.net/~vlivanov/profiling/
[2] http://cr.openjdk.java.net/~vlivanov/8059877/octane.txt
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