Please review this change to the Linux container detection code updating the
mapping function of cg v2 to most recent runtimes' implementation. OCI has been
standardized with cgroup v1 in mind and there is a mapping function in place -
implemented by container runtimes such as `runc` or `crun` - which map the
passed `--cpu-shares` value on the engine's `run` command to the internal
cgroup v2 `cpu.weight` interface file's values.
For runtimes lower than 1.23 (crun) and 1.3.2 (runc) the mapping function was
(where `y=<cpu.weight value>` and `x=<cpu-shares CLI value>`):
f(x) = {(x - 2) \times 9999 + 1 \over 262142}
This changed in `crun` >= 1.23 and `runc` >= 1.3.2 to:
f(x)=10^{({{\log_{2}(x)}^2 \over 612} + {125 \over 612} \times \log_{2}(x) - {7
\over 34})}
Therefore, we need to find the inverse of the new quadratic mapping function
and use that over the inverse of the old mapping function. Since the input
domain is `[2,262144]` for `--cpu-shares` mapping to `[1,10000]` for
`cpu.weight` we can discount the negative exponent value as a possible solution.
Since there are production systems out there with those runtimes already I
believe it's time to change the mapping function internal to the JDK to the new
one in JDK 26. There is a chance that JDK 26 would run on old runtimes in a
container using cgroup v2, resulting in wrong diagnostics. The chance of this
happening will decrease over time.
Thoughts?
**Testing:**
- [x] GHA
- [x] `test/hotspot/jtreg/containers` and `test/jdk/jdk/internal/platform` on
cgroup v1 (with an old runtime - code not affected) and on cgroup v2 with a new
runtime. All tests passed.
-------------
Commit messages:
- Fix include
- Add asserts/checks for input domain
- Add regression test for jdk-8370492
- 8370492: [Linux] Update cpu shares to cpu.weight mapping function
Changes: https://git.openjdk.org/jdk/pull/28157/files
Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28157&range=00
Issue: https://bugs.openjdk.org/browse/JDK-8370492
Stats: 96 lines in 4 files changed: 79 ins; 0 del; 17 mod
Patch: https://git.openjdk.org/jdk/pull/28157.diff
Fetch: git fetch https://git.openjdk.org/jdk.git pull/28157/head:pull/28157
PR: https://git.openjdk.org/jdk/pull/28157
