Migrate github.com/json-iterator/go to sigs.k8s.io/json

[inteon]

fixes #202

Replaces "github.com/json-iterator/go" with "sigs.k8s.io/json" and "encoding/json".

TODO: compare benchmarks before and after <- help would be appreciated here.

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[apelisse]

Yeah, that's ambitious. There's a reason we had written the code the way we did, but let's see what the benchmarks say.

You can do ... IIRC

go test -bench= ./fieldpath/

to run the benchmark. Do that against master and the tip of your branch, save the output in files, run benchstat master.txt pr.txt, see what comes out (you might need to do add a -count=10 to your go test.

[jpbetz]

Benchmarks will be essential here. This code was hyper-optimized because it was on a hot path.

[apelisse]

This is what I get:

> benchstat master.txt pr.txt 
goos: darwin
goarch: arm64
pkg: sigs.k8s.io/structured-merge-diff/v4/fieldpath
                             │  master.txt  │                pr.txt                 │
                             │    sec/op    │    sec/op      vs base                │
FieldSet/serialize-20-14       3.369µ ± ∞ ¹   14.304µ ± ∞ ¹  +324.58% (p=0.008 n=5)
FieldSet/deserialize-20-14     10.18µ ± ∞ ¹    38.24µ ± ∞ ¹  +275.51% (p=0.008 n=5)
FieldSet/serialize-50-14       8.939µ ± ∞ ¹   38.017µ ± ∞ ¹  +325.29% (p=0.008 n=5)
FieldSet/deserialize-50-14     26.22µ ± ∞ ¹   105.66µ ± ∞ ¹  +303.03% (p=0.008 n=5)
FieldSet/serialize-100-14      29.20µ ± ∞ ¹   108.68µ ± ∞ ¹  +272.22% (p=0.008 n=5)
FieldSet/deserialize-100-14    67.92µ ± ∞ ¹   327.90µ ± ∞ ¹  +382.79% (p=0.008 n=5)
FieldSet/serialize-500-14      143.1µ ± ∞ ¹    514.4µ ± ∞ ¹  +259.32% (p=0.008 n=5)
FieldSet/deserialize-500-14    310.6µ ± ∞ ¹   1650.6µ ± ∞ ¹  +431.36% (p=0.008 n=5)
FieldSet/serialize-1000-14     316.4µ ± ∞ ¹   1081.6µ ± ∞ ¹  +241.84% (p=0.008 n=5)
FieldSet/deserialize-1000-14   664.7µ ± ∞ ¹   3654.3µ ± ∞ ¹  +449.78% (p=0.008 n=5)
geomean                        52.16µ          219.8µ        +321.31%
¹ need >= 6 samples for confidence interval at level 0.95

                             │  master.txt   │                 pr.txt                 │
                             │     B/op      │      B/op       vs base                │
FieldSet/serialize-20-14       1.563Ki ± ∞ ¹    8.446Ki ± ∞ ¹  +440.22% (p=0.008 n=5)
FieldSet/deserialize-20-14     9.722Ki ± ∞ ¹   29.034Ki ± ∞ ¹  +198.65% (p=0.008 n=5)
FieldSet/serialize-50-14       4.530Ki ± ∞ ¹   23.527Ki ± ∞ ¹  +419.34% (p=0.008 n=5)
FieldSet/deserialize-50-14     19.94Ki ± ∞ ¹    81.76Ki ± ∞ ¹  +310.11% (p=0.008 n=5)
FieldSet/serialize-100-14      15.67Ki ± ∞ ¹    82.53Ki ± ∞ ¹  +426.74% (p=0.008 n=5)
FieldSet/deserialize-100-14    58.83Ki ± ∞ ¹   300.17Ki ± ∞ ¹  +410.27% (p=0.008 n=5)
FieldSet/serialize-500-14      72.61Ki ± ∞ ¹   396.84Ki ± ∞ ¹  +446.52% (p=0.008 n=5)
FieldSet/deserialize-500-14    270.7Ki ± ∞ ¹   1548.6Ki ± ∞ ¹  +472.07% (p=0.008 n=5)
FieldSet/serialize-1000-14     157.9Ki ± ∞ ¹    845.1Ki ± ∞ ¹  +435.13% (p=0.008 n=5)
FieldSet/deserialize-1000-14   593.6Ki ± ∞ ¹   3325.8Ki ± ∞ ¹  +460.25% (p=0.008 n=5)
geomean                        34.42Ki          170.0Ki        +394.01%
¹ need >= 6 samples for confidence interval at level 0.95

                             │  master.txt  │                 pr.txt                 │
                             │  allocs/op   │   allocs/op    vs base                 │
FieldSet/serialize-20-14        8.000 ± ∞ ¹   334.000 ± ∞ ¹  +4075.00% (p=0.008 n=5)
FieldSet/deserialize-20-14      232.0 ± ∞ ¹     582.0 ± ∞ ¹   +150.86% (p=0.008 n=5)
FieldSet/serialize-50-14        14.00 ± ∞ ¹    926.00 ± ∞ ¹  +6514.29% (p=0.008 n=5)
FieldSet/deserialize-50-14      659.0 ± ∞ ¹    1649.0 ± ∞ ¹   +150.23% (p=0.008 n=5)
FieldSet/serialize-100-14       40.00 ± ∞ ¹   3125.00 ± ∞ ¹  +7712.50% (p=0.008 n=5)
FieldSet/deserialize-100-14    2.298k ± ∞ ¹    5.893k ± ∞ ¹   +156.44% (p=0.008 n=5)
FieldSet/serialize-500-14       185.0 ± ∞ ¹   15607.0 ± ∞ ¹  +8336.22% (p=0.008 n=5)
FieldSet/deserialize-500-14    11.47k ± ∞ ¹    29.62k ± ∞ ¹   +158.09% (p=0.008 n=5)
FieldSet/serialize-1000-14      393.0 ± ∞ ¹   33653.0 ± ∞ ¹  +8463.10% (p=0.008 n=5)
FieldSet/deserialize-1000-14   25.00k ± ∞ ¹    64.48k ± ∞ ¹   +157.87% (p=0.008 n=5)
geomean                         356.2          4.720k        +1225.15%
¹ need >= 6 samples for confidence interval at level 0.95

[jpbetz]

/hold
Thanks @apelisse! Holding based on those numbers to make sure we don't cause a performance regression.

[inteon]

I applied a few hacks and optimisations in 59b4860 and 4f4fbff. These changes improved the performance quite a bit compared to the initial version. However, the performance is still a bit worse than the current version on master (bench.old.txt is master and bench.v1.txt is the latest version of this PR):

$ benchstat bench.old.txt bench.v1.txt 
goos: linux
goarch: amd64
pkg: sigs.k8s.io/structured-merge-diff/v4/fieldpath
cpu: 12th Gen Intel(R) Core(TM) i7-12700H
                            │ bench.old.txt │             bench.v1.txt              │
                            │    sec/op     │    sec/op      vs base                │
FieldSet/serialize-20-6        3.526µ ± ∞ ¹    7.008µ ± ∞ ¹   +98.75% (p=0.029 n=4)
FieldSet/deserialize-20-6      9.038µ ± ∞ ¹   16.972µ ± ∞ ¹   +87.78% (p=0.029 n=4)
FieldSet/serialize-50-6        11.14µ ± ∞ ¹    19.83µ ± ∞ ¹   +78.06% (p=0.029 n=4)
FieldSet/deserialize-50-6      25.43µ ± ∞ ¹    52.32µ ± ∞ ¹  +105.80% (p=0.029 n=4)
FieldSet/serialize-100-6       39.24µ ± ∞ ¹    68.09µ ± ∞ ¹   +73.52% (p=0.029 n=4)
FieldSet/deserialize-100-6     86.16µ ± ∞ ¹   181.32µ ± ∞ ¹  +110.44% (p=0.029 n=4)
FieldSet/serialize-500-6       202.0µ ± ∞ ¹    358.5µ ± ∞ ¹   +77.47% (p=0.029 n=4)
FieldSet/deserialize-500-6     412.8µ ± ∞ ¹    868.4µ ± ∞ ¹  +110.33% (p=0.029 n=4)
FieldSet/serialize-1000-6      473.1µ ± ∞ ¹    860.7µ ± ∞ ¹   +81.93% (p=0.029 n=4)
FieldSet/deserialize-1000-6    822.5µ ± ∞ ¹   1984.8µ ± ∞ ¹  +141.31% (p=0.029 n=4)
geomean                        63.03µ          123.3µ         +95.57%
¹ need >= 6 samples for confidence interval at level 0.95

                            │ bench.old.txt │              bench.v1.txt              │
                            │     B/op      │      B/op       vs base                │
FieldSet/serialize-20-6       1.536Ki ± ∞ ¹    1.621Ki ± ∞ ¹    +5.53% (p=0.029 n=4)
FieldSet/deserialize-20-6     9.745Ki ± ∞ ¹   15.893Ki ± ∞ ¹   +63.09% (p=0.029 n=4)
FieldSet/serialize-50-6       4.463Ki ± ∞ ¹    4.282Ki ± ∞ ¹    -4.05% (p=0.029 n=4)
FieldSet/deserialize-50-6     20.02Ki ± ∞ ¹    46.73Ki ± ∞ ¹  +133.43% (p=0.029 n=4)
FieldSet/serialize-100-6      15.71Ki ± ∞ ¹    16.22Ki ± ∞ ¹    +3.28% (p=0.029 n=4)
FieldSet/deserialize-100-6    58.98Ki ± ∞ ¹   164.79Ki ± ∞ ¹  +179.39% (p=0.029 n=4)
FieldSet/serialize-500-6      72.84Ki ± ∞ ¹    64.28Ki ± ∞ ¹   -11.75% (p=0.029 n=4)
FieldSet/deserialize-500-6    270.1Ki ± ∞ ¹    842.0Ki ± ∞ ¹  +211.73% (p=0.029 n=4)
FieldSet/serialize-1000-6     154.4Ki ± ∞ ¹    128.3Ki ± ∞ ¹   -16.91% (p=0.029 n=4)
FieldSet/deserialize-1000-6   593.1Ki ± ∞ ¹   1805.6Ki ± ∞ ¹  +204.42% (p=0.029 n=4)
geomean                       34.27Ki          52.94Ki         +54.48%
¹ need >= 6 samples for confidence interval at level 0.95

                            │ bench.old.txt │            bench.v1.txt             │
                            │   allocs/op   │  allocs/op    vs base               │
FieldSet/serialize-20-6         8.000 ± ∞ ¹    7.000 ± ∞ ¹  -12.50% (p=0.029 n=4)
FieldSet/deserialize-20-6       231.0 ± ∞ ¹    253.0 ± ∞ ¹   +9.52% (p=0.029 n=4)
FieldSet/serialize-50-6        14.000 ± ∞ ¹    9.000 ± ∞ ¹  -35.71% (p=0.029 n=4)
FieldSet/deserialize-50-6       661.0 ± ∞ ¹    743.5 ± ∞ ¹  +12.48% (p=0.029 n=4)
FieldSet/serialize-100-6        40.00 ± ∞ ¹    10.00 ± ∞ ¹  -75.00% (p=0.029 n=4)
FieldSet/deserialize-100-6     2.296k ± ∞ ¹   2.611k ± ∞ ¹  +13.74% (p=0.029 n=4)
FieldSet/serialize-500-6       184.00 ± ∞ ¹    13.00 ± ∞ ¹  -92.93% (p=0.029 n=4)
FieldSet/deserialize-500-6     11.48k ± ∞ ¹   13.07k ± ∞ ¹  +13.85% (p=0.029 n=4)
FieldSet/serialize-1000-6      392.50 ± ∞ ¹    14.00 ± ∞ ¹  -96.43% (p=0.029 n=4)
FieldSet/deserialize-1000-6    24.99k ± ∞ ¹   28.52k ± ∞ ¹  +14.12% (p=0.029 n=4)
geomean                         355.8          170.7        -52.03%
¹ need >= 6 samples for confidence interval at level 0.95

[jpbetz]

For context, there were quite a few months of engineering effort to optimize the performance of SSA, and in particular, managed fields. I'm supportive of making this code better, but I feel responsible to ensure that we don't regress significantly here.

[inteon]

For context, there were quite a few months of engineering effort to optimize the performance of SSA, and in particular, managed fields. I'm supportive of making this code better, but I feel responsible to ensure that we don't regress significantly here.

This PR aims to be the very best attempt at making #202 work. If we do achieve the required performance, this PR will be the proof that it is not possible to switch to the "encoding/json" package unless the performance of that package is improved.

[k8s-ci-robot]

@inteon: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-structured-merge-diff-vet	26b5747	link	true	/test pull-structured-merge-diff-vet

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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[dominiquelefevre]

For context, there were quite a few months of engineering effort

For more context, modern-go/reflect2 and json-iterator/go are both unmaintained and broken. #202 documents one problem with reflect2. There are more. For example, it uses some braindead constructs that make it impossible for golang to apply dead code elimination to anything that depends on reflect2, even transitively. Since structured-merge-diff and k8s.io/apimachinery are dependencies of everything that uses k8s, reflect2 hurts everyone by inhibiting the DCE.

reflect2 is the cause of more trouble. For example, see golang/go@ef225d1. I very much regret it that golang authors chose to fix reflect2 when releasing go 1.18, and keep adding kludges.

Suck it up and be correct first.

[apelisse]

Suck it up and be correct first.

I don't get it, what are we supposed to suck up? And who is even supposed to?

Are we supposed to suck up the performance impact, or are we supposed to get it done somehow?

[apelisse]

@liggitt In 2024, what's the best json library in Go to build a json part by part and stream it directly rather than serialize everything in a big string?

[apelisse]

Gojay seems like a good alternative, it seems to have good performance, custom encoding/decoding, and a streaming API: https://github.com/francoispqt/gojay

[liggitt]

if we were going to pull in another json library, I'd aim for the same one we used in kube-openapi (https://github.com/kubernetes/kube-openapi/tree/master/pkg/internal/third_party/go-json-experiment) since that's where it looks like the stdlib is headed (golang/go#63397) and supports streaming / custom encoding/decoding, etc

[liggitt]

really not a fan of adding unsafe usages

[liggitt]

really not a fan of point-in-time copies of runtime code that could become unsafe in the future

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