cmd/go/internal/work: add telemetry counters for build cache hits/misses

The following counters are added in this cl
    go/buildcache/hit
    go/buildcache/miss
    go/buildcache/stdlibrecompiled (incremented at most once per
        invocation)

Change-Id: Ia78e136feac8226cb35e554503b672343cc30262
Reviewed-on: https://go-review.googlesource.com/c/go/+/587577
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-by: Sam Thanawalla <samthanawalla@google.com>

diff --git a/src/cmd/go/internal/work/buildid.go b/src/cmd/go/internal/work/buildid.go
index acbda1af5532ed56465ca6caf832ff51a1ed3551..889cc6ca508ef706a9b1bec375562a2146af4bd6 100644 (file)
--- a/src/cmd/go/internal/work/buildid.go
+++ b/src/cmd/go/internal/work/buildid.go
@@ -10,6 +10,7 @@ import (
        "os"
        "os/exec"
        "strings"
+       "sync"
 
        "cmd/go/internal/base"
        "cmd/go/internal/cache"
@@ -18,6 +19,7 @@ import (
        "cmd/go/internal/str"
        "cmd/internal/buildid"
        "cmd/internal/quoted"
+       "cmd/internal/telemetry"
 )
 
 // Build IDs
@@ -403,6 +405,14 @@ func (b *Builder) fileHash(file string) string {
        return buildid.HashToString(sum)
 }
 
+var (
+       counterCacheHit  = telemetry.NewCounter("go/buildcache/hit")
+       counterCacheMiss = telemetry.NewCounter("go/buildcache/miss")
+
+       onceIncStdlibRecompiled sync.Once
+       stdlibRecompiled        = telemetry.NewCounter("go/buildcache/stdlib-recompiled")
+)
+
 // useCache tries to satisfy the action a, which has action ID actionHash,
 // by using a cached result from an earlier build. At the moment, the only
 // cached result is the installed package or binary at target.
@@ -416,7 +426,7 @@ func (b *Builder) fileHash(file string) string {
 // during a's work. The caller should defer b.flushOutput(a), to make sure
 // that flushOutput is eventually called regardless of whether the action
 // succeeds. The flushOutput call must happen after updateBuildID.
-func (b *Builder) useCache(a *Action, actionHash cache.ActionID, target string, printOutput bool) bool {
+func (b *Builder) useCache(a *Action, actionHash cache.ActionID, target string, printOutput bool) (ok bool) {
        // The second half of the build ID here is a placeholder for the content hash.
        // It's important that the overall buildID be unlikely verging on impossible
        // to appear in the output by chance, but that should be taken care of by
@@ -448,6 +458,20 @@ func (b *Builder) useCache(a *Action, actionHash cache.ActionID, target string,
                return false
        }
 
+       defer func() {
+               // Increment counters for cache hits and misses based on the return value
+               // of this function. Don't increment counters if we return early because of
+               // cfg.BuildA above because we don't even look at the cache in that case.
+               if ok {
+                       counterCacheHit.Inc()
+               } else {
+                       if a.Package != nil && a.Package.Standard {
+                               onceIncStdlibRecompiled.Do(stdlibRecompiled.Inc)
+                       }
+                       counterCacheMiss.Inc()
+               }
+       }()
+
        c := cache.Default()
 
        if target != "" {