RFR: 8372701: Randomized profile counters [v9]

[Andrew Haley]

> Please use [this link](https://github.com/openjdk/jdk/pull/28541/changes?w=1) to view the files changed.
> 
> Profile counters scale very badly.
> 
> The overhead for profiled code isn't too bad with one thread, but as the thread count increases, things go wrong very quickly.
> 
> For example, here's a benchmark from the OpenJDK test suite, run at TieredLevel 3 with one thread, then three threads:
> 
> 
> Benchmark (randomized) Mode Cnt Score Error Units
> InterfaceCalls.test2ndInt5Types false avgt 4 27.468 ± 2.631 ns/op
> InterfaceCalls.test2ndInt5Types false avgt 4 240.010 ± 6.329 ns/op
> 
> 
> This slowdown is caused by high memory contention on the profile counters. Not only is this slow, but it can also lose profile counts.
> 
> This patch is for C1 only. It'd be easy to randomize C1 counters as well in another PR, if anyone thinks it's worth doing.
> 
> One other thing to note is that randomized profile counters degrade very badly with small decimation ratios. For example, using a ratio of 2 with `-XX:ProfileCaptureRatio=2` with a single thread results in
> 
> 
> Benchmark                        (randomized)  Mode  Cnt   Score   Error  Units
> InterfaceCalls.test2ndInt5Types         false  avgt    4  80.147 ± 9.991  ns/op
> 
> 
> The problem is that the branch prediction rate drops away very badly, leading to many mispredictions. It only really makes sense to use higher decimation ratios, e.g. 64.

Andrew Haley has updated the pull request incrementally with four additional commits since the last revision:

 - Checkpoint
 - Seems to work
 - Checkpoint
 - Seems to work

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/28541/files
  - new: https://git.openjdk.org/jdk/pull/28541/files/2a0cb808..94b4e56a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=28541&range=08
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=28541&range=07-08

  Stats: 560 lines in 10 files changed: 229 ins; 240 del; 91 mod
  Patch: https://git.openjdk.org/jdk/pull/28541.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28541/head:pull/28541

PR: https://git.openjdk.org/jdk/pull/28541