original-brownbear commented on code in PR #13936:
URL: https://github.com/apache/lucene/pull/13936#discussion_r1807955670
##########
lucene/core/src/java/org/apache/lucene/util/PriorityQueue.java:
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@@ -270,7 +280,7 @@ public final boolean remove(T element) {
return false;
}
- private final boolean upHeap(int origPos) {
+ private boolean upHeap(int origPos, T[] heap) {
Review Comment:
Whether or not it's worth doing this kind of optimization for the observed
gain is a tricky question. From the perspective of a user of a large (and
read-heavy) ES, Opensearch or similar deployment, an O(1%) gain might translate
into a lot of dollars saved and this kind of thing is well worth the effort.
Personally, an extra 10 lines of code for the observed speedups seems like a
reasonable deal, but that's admittedly quite subjective. Maybe a stronger
argument would be: optimizing this kind of thing in core hot code removes
potential bottlenecks from the system, enabling other optimizations. If the
core logic puts massive pressure on e.g. the CPU cache then optimizations (or
regressions!) in higher-level code are masked on CPUs with smaller caches. So
doing a 1% optimization and living with slightly more complicated code makes
more sense here than a 1% gain would in more "peripheral" code. Also, you could
use that same angle and argue that this code hardly ever gets touched, so the
maintenance burden added matters less than it would elsewhere.
That said :) as far as the technical details go I don't think it can hoist
out those reads and it's not an exclusively C2/hotstpot specific thing either.
Since Java allows using reflection to update final field values (except for
fields that are either static, on a record or on a hidden classs) the compiler
can't hoist the field access out of the loop I think (maybe in some happy cases
escape analysis helps here).
You can make the JIT hoist these things via `-XX:+TrustFinalNonStaticFields`
which gives me a result like (main vs main with that flag set).
<details>
<summary>results</summary>
<pre>
TaskQPS baseline StdDevQPS
my_modified_version StdDev Pct diff p-value
HighTermTitleBDVSort 25.72 (7.0%) 25.77
(6.5%) 0.2% ( -12% - 14%) 0.897
BrowseRandomLabelSSDVFacets 3.37 (6.0%) 3.40
(4.2%) 1.0% ( -8% - 11%) 0.409
OrHighMed 214.06 (3.7%) 216.37
(3.8%) 1.1% ( -6% - 8%) 0.206
OrHighNotHigh 353.55 (8.4%) 358.52
(8.9%) 1.4% ( -14% - 20%) 0.475
AndHighHigh 111.32 (4.9%) 113.08
(5.5%) 1.6% ( -8% - 12%) 0.179
OrNotHighHigh 567.88 (4.8%) 577.94
(4.9%) 1.8% ( -7% - 12%) 0.108
PKLookup 241.21 (2.1%) 245.53
(2.1%) 1.8% ( -2% - 6%) 0.000
HighTerm 455.94 (6.6%) 464.35
(7.5%) 1.8% ( -11% - 17%) 0.250
MedTerm 590.06 (6.5%) 601.24
(6.0%) 1.9% ( -9% - 15%) 0.182
AndHighMed 156.22 (3.1%) 159.19
(2.9%) 1.9% ( -3% - 8%) 0.005
LowTerm 750.87 (4.6%) 765.45
(4.2%) 1.9% ( -6% - 11%) 0.052
BrowseRandomLabelTaxoFacets 4.48 (8.6%) 4.57
(3.9%) 2.0% ( -9% - 15%) 0.182
OrNotHighMed 479.29 (4.6%) 489.00
(5.4%) 2.0% ( -7% - 12%) 0.074
HighTermMonthSort 1515.68 (6.4%) 1546.97
(7.0%) 2.1% ( -10% - 16%) 0.171
OrHighHigh 85.48 (4.6%) 87.32
(5.3%) 2.2% ( -7% - 12%) 0.055
MedTermDayTaxoFacets 19.13 (3.0%) 19.55
(4.1%) 2.2% ( -4% - 9%) 0.007
MedIntervalsOrdered 28.59 (6.3%) 29.23
(4.7%) 2.2% ( -8% - 14%) 0.079
OrHighLow 610.70 (5.0%) 624.94
(5.0%) 2.3% ( -7% - 13%) 0.040
OrHighNotMed 474.52 (5.5%) 485.78
(5.7%) 2.4% ( -8% - 14%) 0.061
Fuzzy2 66.51 (3.2%) 68.09
(3.0%) 2.4% ( -3% - 8%) 0.001
BrowseDateSSDVFacets 1.24 (7.7%) 1.27
(8.1%) 2.4% ( -12% - 19%) 0.181
MedSpanNear 119.05 (4.4%) 121.94
(4.4%) 2.4% ( -6% - 11%) 0.016
HighTermTitleSort 76.83 (4.8%) 78.72
(3.7%) 2.5% ( -5% - 11%) 0.011
AndHighHighDayTaxoFacets 14.60 (3.8%) 14.96
(3.5%) 2.5% ( -4% - 10%) 0.003
BrowseMonthTaxoFacets 11.04 (38.5%) 11.32
(40.3%) 2.5% ( -55% - 132%) 0.778
OrNotHighLow 1089.24 (4.0%) 1117.30
(4.0%) 2.6% ( -5% - 10%) 0.004
TermDTSort 188.79 (4.6%) 193.74
(4.9%) 2.6% ( -6% - 12%) 0.015
Wildcard 426.59 (4.2%) 437.79
(4.2%) 2.6% ( -5% - 11%) 0.006
MedPhrase 78.10 (3.4%) 80.38
(3.2%) 2.9% ( -3% - 9%) 0.000
Prefix3 1068.70 (7.7%) 1100.07
(7.7%) 2.9% ( -11% - 19%) 0.094
AndHighLow 1546.10 (5.3%) 1591.97
(6.0%) 3.0% ( -7% - 15%) 0.020
LowIntervalsOrdered 134.11 (6.2%) 138.10
(5.0%) 3.0% ( -7% - 15%) 0.019
MedSloppyPhrase 47.07 (4.5%) 48.49
(3.7%) 3.0% ( -5% - 11%) 0.001
AndHighMedDayTaxoFacets 65.36 (2.3%) 67.38
(2.3%) 3.1% ( -1% - 7%) 0.000
LowSpanNear 175.93 (3.7%) 181.36
(4.7%) 3.1% ( -5% - 11%) 0.001
HighPhrase 131.54 (7.2%) 135.70
(5.8%) 3.2% ( -9% - 17%) 0.033
Fuzzy1 108.08 (3.4%) 111.62
(2.1%) 3.3% ( -2% - 9%) 0.000
BrowseDayOfYearSSDVFacets 4.52 (7.7%) 4.67
(7.9%) 3.4% ( -11% - 20%) 0.056
OrHighNotLow 550.21 (7.0%) 569.01
(7.9%) 3.4% ( -10% - 19%) 0.043
HighTermDayOfYearSort 380.03 (7.6%) 393.27
(6.6%) 3.5% ( -9% - 19%) 0.030
HighSpanNear 11.37 (4.5%) 11.77
(6.0%) 3.5% ( -6% - 14%) 0.004
Respell 54.77 (1.6%) 56.69
(1.7%) 3.5% ( 0% - 6%) 0.000
HighSloppyPhrase 30.28 (5.2%) 31.40
(4.8%) 3.7% ( -5% - 14%) 0.001
LowPhrase 76.63 (5.6%) 79.65
(5.6%) 3.9% ( -6% - 16%) 0.002
OrHighMedDayTaxoFacets 6.78 (6.2%) 7.05
(6.9%) 4.0% ( -8% - 18%) 0.007
IntNRQ 78.26 (6.5%) 81.38
(7.2%) 4.0% ( -9% - 18%) 0.010
LowSloppyPhrase 65.45 (6.6%) 68.14
(6.0%) 4.1% ( -7% - 17%) 0.004
HighIntervalsOrdered 9.16 (6.5%) 9.59
(5.9%) 4.6% ( -7% - 18%) 0.001
BrowseMonthSSDVFacets 4.48 (10.4%) 4.70
(12.4%) 4.8% ( -16% - 30%) 0.062
BrowseDateTaxoFacets 5.38 (10.8%) 5.67
(12.7%) 5.4% ( -16% - 32%) 0.043
BrowseDayOfYearTaxoFacets 5.44 (10.6%) 5.74
(12.7%) 5.5% ( -16% - 32%) 0.039
</pre>
</details>
So to me it feels like manually hoisting field access is a generally valid
optimization in a world that has reflective writes to final fields. To me,
reducing field access is not in the same category as e.g. extracting cold paths
artifically to make a method inline or other such tricks that are specific to
C2 and hardware. This is just giving the compiler input that it cannot
practically work out with the constraints imposed by the language and the JIT's
runtime cost needing
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