[NOT TO MERGE YET] 8258604: Use 'isb' instruction in SpinPause on linux-aarch64

[eastig]

To implement SpinPause an instruction creating a small delay without consuming ALU resources is needed. AArch64 has the YIELD instruction but most of AArch64 vendors still implement it as a NOP. It's been found that ISB can create a small delay without consuming ALU resources. It is more reliable than NOPs.

This patch implements SpinPause with ISB.
Testing: gtest, tier1, tier2

Results of https://github.com/ben-manes/caffeine/wiki/Benchmarks

GetPutBenchmark has 8 threads concurrently working with a cache.
GetPutBenchmark.read_only all 8 thread read from a cache.
GetPutBenchmark.write_only all 8 thread write to a cache.
GetPutBenchmark.readwrite 6 threads concurrently read from and 2 threads write to a cache.

Improvements when only 4 CPUs are available:

(cacheType)         Benchmark                               Units    Baseline       Error           CoV     New             Error           CoV     New vs Base
Cache2k             GetPutBenchmark.readwrite:readwrite_get ops/s   58,893,980.32   1,903,084.75    3.23%   65,685,338.20   4,858,329.69    7.40%   11.5%
ExpiringMap_Fifo    GetPutBenchmark.read_only               ops/s   5,060,227.98    695,582.74      13.75%  6,040,948.02    1,046,581.70    17.32%  19.4%
ExpiringMap_Fifo    GetPutBenchmark.readwrite:readwrite_put ops/s   433,046.21      194,297.64      44.87%  783,825.18      272,868.60      34.81%  81.0%
LinkedHashMap_Lru   GetPutBenchmark.read_only               ops/s   6,405,770.38    607,772.98      9.49%   10,259,858.51   1,446,471.70    14.10%  60.2%
LinkedHashMap_Lru   GetPutBenchmark.readwrite:readwrite_get ops/s   3,083,275.32    400,878.84      13.00%  5,934,784.52    1,309,784.39    22.07%  92.5%
LinkedHashMap_Lru   GetPutBenchmark.readwrite:readwrite_put ops/s   1,669,852.29    356,469.07      21.35%  2,491,807.50    299,230.23      12.01%  49.2%
LinkedHashMap_Lru   GetPutBenchmark.write_only              ops/s   4,623,049.93    449,438.94      9.72%   7,069,151.98    1,725,457.51    24.41%  52.9%

Improvements when only 8 CPUs are available:

(cacheType)         Benchmark                               Units    Baseline       Error       CoV     New             Error       CoV      New vs Base
LinkedHashMap_Lru   GetPutBenchmark.read_only               ops/s   4,054,507.30    71,693.81   1.77%   4,306,745.31    226,212.96  5.25%   6.2%
LinkedHashMap_Lru   GetPutBenchmark.readwrite:readwrite_get ops/s   3,087,578.38    86,158.78   2.79%   2,818,742.51    301,261.76  10.69%  -8.7%
LinkedHashMap_Lru   GetPutBenchmark.readwrite:readwrite_put ops/s   1,053,560.98    66,412.90   6.30%   1,401,928.05    239,055.34  17.05%  33.1%
LinkedHashMap_Lru   GetPutBenchmark.write_only              ops/s   3,823,208.44    305,096.58  7.98%   4,510,823.31    390,622.00  8.66%   18.0%

LinkedHashMapCache source
Cache2k source
ExpiringMapCache source
GetPutBenchmark source

---

Progress

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Reviewers

• Paul Hohensee (@phohensee - Reviewer)

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[bridgekeeper]

👋 Welcome back eastig! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

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[mlbridge]

Webrevs

• 01: Full - Incremental (d9febbdf)
• 00: Full (31808c6b)

[phohensee]

SpinPause() should return 1 if it executes code. See the x86/64 implementations.

[openjdk]

@eastig This change is no longer ready for integration - check the PR body for details.

[eastig]

/integrate

[openjdk]

@eastig
Your change (at version d9febbd) is now ready to be sponsored by a Committer.

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[stooart-mon]

I hadn't realised this was unconditional. Similar to my comment on the onSpinWait patch, while the ISB instruction happens to work for you just now on the platforms you have tested, there is no guarantee that it will continue to do so in future processors.
Could this be made optional? This is awkward, as it is C++ code, but it may have to be a build configuration option.

[eastig]

Hi Stuart,
Yes, I'll be updating it to support different implementations.

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