Backport of scheduler: don't sort reserved port ranges before adding to bitmap into release/1.10.x

[hc-github-team-nomad-core]

Backport

This PR is auto-generated from #26712 to be assessed for backporting due to the inclusion of the label backport/1.10.x.

The below text is copied from the body of the original PR.

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During a large volume dispatch load test, I discovered that a lot of the total scheduling time is being spent calling structs.ParsePortRanges repeatedly, in order to parse the reserved ports configuration of the node (ex. converting "80,8000-8001" to []int{80, 8000, 8001}). A close examination of the profiles shows that the bulk of the time is being spent hashing the keys for the map of ports we use for de-duplication, and then sorting the resulting slice.

The (*NetworkIndex) SetNode method that calls the offending ParsePortRanges merges all the ports into the UsedPorts map of bitmaps at scheduling time. Which means the consumer of the slice is already de-duplicating and doesn't care about the order. The only other caller of ParsePortRanges is when we validate the configuration file, and that throws away the slice entirely.

By skipping de-duplication and not sorting, we can cut down the runtime of this function by 30x and memory usage by 4x.

See my comment here for why memoizing the result proved to be impractical. This changeset also deletes the unused ParseReservedHostPorts method and moves its tests into the tests for ParsePortRanges (which is really what it was testing anyways).

Ref: https://github.com/hashicorp/nomad/blob/v1.10.4/nomad/structs/network.go#L201
Fixes: #26654

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I'm going to reproduce the test I ran that I've described in #26654 but in the meantime, here's a microbenchmark:

func BenchmarkParsePortRangesOld(b *testing.B) {
       spec := "22,8000-9000"
       for b.Loop() {
               ParsePortRanges(spec)
       }
}

func BenchmarkParsePortRangesNew(b *testing.B) {
       spec := "22,8000-9000"
       for b.Loop() {
               ParsePortRangesNew(spec)
       }
}

$ go test -v -count=1 ./nomad/structs -benchmem -bench BenchmarkParsePortRanges -run=^#
goos: linux
goarch: amd64
pkg: github.com/hashicorp/nomad/nomad/structs
cpu: Intel(R) Core(TM) Ultra 7 165H
BenchmarkParsePortRangesOld
BenchmarkParsePortRangesOld-22              7041            149205 ns/op           99616 B/op         37 allocs/op
BenchmarkParsePortRangesNew
BenchmarkParsePortRangesNew-22            233440              4926 ns/op           25288 B/op         15 allocs/op
PASS
ok      github.com/hashicorp/nomad/nomad/structs        2.214s

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Overview of commits

• f86a141