Go - Save up to 14% CPU in Production with Profile-Guided Optimization

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Overview

Starting with [Go 1.21][1], the Go compiler supports profile-guided optimization (PGO).

PGO enables additional optimizations on code identified as hot by CPU profiles of production workloads. This is compatible with [Datadog Go Continuous Profiler][2] and can be used for production builds.

How PGO works

Here are some key points about how PGO works:

Building a Go program with PGO enabled causes the compiler to look for a pprof CPU profile named default.pgo and use it to produce a more optimized binary.
Typical programs should see a 2-14% decrease in CPU time after optimization. PGO remains under active development, and future versions of Go aim to achieve even greater CPU savings. Datadog is [actively supporting this initiative][3].
PGO produces the best results when using representative profiles. However, using non-representative or old profiles (from previous versions of the software) is not expected to result in slower binaries compared to not using PGO.
Using a profile from a PGO optimized application is not expected to cause optimization/deoptimization cycles. This is referred to as iterative stability.

For more information, see the [Go PGO documentation][4].

Enabling PGO

PGO is a standard Go compiler option that you can use by manually downloading profiles from Datadog. Datadog built a tool, datadog-pgo to help you enable PGO on all services, using the latest and most representative profiles.

datadog-pgo is in public beta.

To enable PGO using the datadog-pgo tool:

Create a dedicated API key and an application key scoped to at least continuous_profiler_pgo_read as described in [API and Application Keys][5].
Set DD_API_KEY, DD_APP_KEY, and DD_SITE with the environment secret mechanism of your CI provider.
Run datadog-pgo before your build step. For example, for a service foo that runs in prod and has its main package in ./cmd/foo, you should add this step:
```
go run github.com/DataDog/datadog-pgo@latest "service:foo env:prod" ./cmd/foo/default.pgo
```