Change defaults of --jit options

* --jit-min-calls: 5 -> 10000

--jit-min-calls=5 obviously can compile non hotspot. This was not a
problem for MJIT-benchmarks and Optcarrot because the former has very
few hot optimiziable methods and the latter is likely to trigger
compilation of hotspot by its intensive calls to optimizable hotspot
methods and has a very short window to allow limited compilations.

In real-world applications, it has more time to compile more methods and
it pressures computer's limited resources like icache. We should avoid
compiling too many methods. Also compiling many methods exhausts time
budget for compilation in one ruby process lifetime and delays the "JIT
compaction" of Ruby 2.6.

JVM is known to use 1,500 for C1 (client) compiler and 10,000 for C2
(server) compiler for -XX:CompileThreshold by default.
https://docs.oracle.com/javase/8/embedded/develop-apps-platforms/codecache.htm

When things are called X,000 times, requiring 10,000 can eliminate
compilation of methods which are called only once in these X,000
iterations and obviously not hotspot. And in fact things like
unicorn-worker-killer restarts unicorn process every 4096 requests.
So I felt 10,000 is good for such an environment.

* --jit-max-cache: 1000 -> 100

By the same reason stated above, we should not allow compiling many
methods especially on MJIT which has a larger overhead due to poor code
locality by dlopen and whose code is also likely to be bigger by just
inlining many VM instructions with -O3 rather than directly generating
low-level code.

In JVM -XX:ReservedCodeCacheSize is 32M for reserved and 48M for maximum.
--jit-max-cache=1,000 could be closer to it, but in this case MJIT's
compilation is slow due to data synchronization between threads (to be
improved in Ruby 2.7 though) and we do not want to delay the "JIT
compaction" for a long time.

So I chose a really conservative number for this, but by having method
inlining in the future, wider range could be optimized even with this
value.

* Optcarrot

--disable-gems, --benchmark Lan_Master.nes 12 attempts.
No significant impact.

| r67276             | r67276 --jit      | after --jit       |
|:-------------------|:------------------|:------------------|
| 50.44369263063978  | 72.87390680773056 | 73.47873485047297 |
| 50.58788746124193  | 78.06820808947026 | 78.29723420171945 |
| 50.77509250801378  | 80.29010348842613 | 78.94689404460769 |
| 50.935361702064405 | 80.42796829926374 | 80.39539527351525 |
| 51.27352672981195  | 81.98758158033202 | 81.6754198664817  |
| 51.720715743242124 | 82.00118535811626 | 82.22960569251283 |
| 51.89643169822524  | 82.2290091613556  | 82.5013636146388  |
| 51.95895898113868  | 82.37318990939565 | 82.74002377794454 |
| 52.10124886807968  | 82.48796686037502 | 83.23354941183932 |
| 52.292280637519376 | 83.0265226541066  | 84.01552618012572 |
| 52.51856237784144  | 83.8797360318052  | 84.8588319093393  |
| 52.65076845986818  | 84.80037351256634 | 85.13577756273656 |

* Railsbench

`WARMUP=20000 BENCHMARK=1000 bin/bench` of https://github.com/k0kubun/railsbench.
It gets closer to --disable=jit.

|           | r67276 | r67276 | after  |
|           |        | --jit  | --jit  |
|:----------|:-------|:-------|:-------|
| req/s     | 891.3  | 742.2  | 841.5  |
|:----------|:-------|:-------|:-------|
| 50%ile ms | 1.00   | 1.21   | 1.08   |
| 66%ile ms | 1.02   | 1.24   | 1.09   |
| 75%ile ms | 1.03   | 1.28   | 1.10   |
| 80%ile ms | 1.03   | 1.30   | 1.11   |
| 90%ile ms | 1.09   | 1.42   | 1.15   |
| 95%ile ms | 1.32   | 1.65   | 1.27   |
| 98%ile ms | 4.79   | 2.23   | 1.81   |
| 99%ile ms | 5.68   | 7.52   | 6.64   |
|100%ile ms | 6.52   | 9.69   | 8.59   |

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@67277 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 2 insertions, 2 deletions

diff --git a/ruby.c b/ruby.c
index 28afa4cfc0..d6456272a1 100644
--- a/ruby.c
+++ b/ruby.c
@@ -287,8 +287,8 @@ usage(const char *name, int help)
         M("--jit-wait",          "", "Wait until JIT compilation is finished everytime (for testing)"),
         M("--jit-save-temps",    "", "Save JIT temporary files in $TMP or /tmp (for testing)"),
         M("--jit-verbose=num",   "", "Print JIT logs of level num or less to stderr (default: 0)"),
-        M("--jit-max-cache=num", "", "Max number of methods to be JIT-ed in a cache (default: 1000)"),
-        M("--jit-min-calls=num", "", "Number of calls to trigger JIT (for testing, default: 5)"),
+        M("--jit-max-cache=num", "", "Max number of methods to be JIT-ed in a cache (default: 100)"),
+        M("--jit-min-calls=num", "", "Number of calls to trigger JIT (for testing, default: 10000)"),
     };
     int i;
     const int num = numberof(usage_msg) - (help ? 1 : 0);