cli: Set GOMAXPROCS on start if in a CPU-limited cgroup

pkg/cli/BUILD.bazel

@@ -136,6 +136,7 @@ go_library(
         "//pkg/storage/enginepb",
         "//pkg/ts/tspb",
         "//pkg/util",
+        "//pkg/util/cgroups",
         "//pkg/util/contextutil",
         "//pkg/util/encoding",
         "//pkg/util/encoding/csv",

pkg/cli/start.go

@@ -39,6 +39,7 @@ import (
 	"github.com/cockroachdb/cockroach/pkg/settings/cluster"
 	"github.com/cockroachdb/cockroach/pkg/storage"
 	"github.com/cockroachdb/cockroach/pkg/storage/enginepb"
+	"github.com/cockroachdb/cockroach/pkg/util/cgroups"
 	"github.com/cockroachdb/cockroach/pkg/util/envutil"
 	"github.com/cockroachdb/cockroach/pkg/util/grpcutil"
 	"github.com/cockroachdb/cockroach/pkg/util/hlc"
@@ -359,6 +360,11 @@ func runStart(cmd *cobra.Command, args []string, startSingleNode bool) (returnEr
 	// but when actually starting a server, we enable them.
 	grpcutil.LowerSeverity(severity.WARNING)
 
+	// Tweak GOMAXPROCS if we're in a cgroup / container that has cpu limits set.
+	// The GO default for GOMAXPROCS is runtime.NumCPU(), however this is less
+	// than ideal if the cgruop is limited to a number lower than that.
+	cgroups.AdjustMaxProcs(ctx)
+
 	// Check the --join flag.
 	if !flagSetForCmd(cmd).Lookup(cliflags.Join.Name).Changed {
 		err := errors.WithHint(

pkg/testutils/lint/lint_test.go

@@ -446,6 +446,7 @@ func TestLint(t *testing.T) {
 					":!ccl/workloadccl/fixture_test.go",
 					":!internal/gopath/gopath.go",
 					":!cmd",
+					":!util/cgroups/cgroups.go",
 					":!nightly",
 					":!testutils/lint",
 					":!util/envutil/env.go",

pkg/util/cgroups/BUILD.bazel

@@ -5,7 +5,10 @@ go_library(
     srcs = ["cgroups.go"],
     importpath = "github.com/cockroachdb/cockroach/pkg/util/cgroups",
     visibility = ["//visibility:public"],
-    deps = ["//vendor/github.com/cockroachdb/errors"],
+    deps = [
+        "//pkg/util/log",
+        "//vendor/github.com/cockroachdb/errors",
+    ],
 )
 
 go_test(

pkg/util/cgroups/cgroups.go

@@ -13,6 +13,7 @@ package cgroups
 import (
 	"bufio"
 	"bytes"
+	"context"
 	"fmt"
 	"io/ioutil"
 	"math"
@@ -22,6 +23,7 @@ import (
 	"strconv"
 	"strings"
 
+	"github.com/cockroachdb/cockroach/pkg/util/log"
 	"github.com/cockroachdb/errors"
 )
 
@@ -444,3 +446,20 @@ func getCgroupCPU(root string) (CPUUsage, error) {
 
 	return res, nil
 }
+
+// AdjustMaxProcs sets GOMAXPROCS (if not overridden by env variables) to be
+// the CPU limit of the current cgroup, if running inside a cgroup with a cpu
+// limit lower than runtime.NumCPU(). This is preferable to letting it fall back
+// to Go default, which is runtime.NumCPU(), as the Go scheduler would be
+// running more OS-level threads than can ever be concurrently scheduled.
+func AdjustMaxProcs(ctx context.Context) {
+	if _, set := os.LookupEnv("GOMAXPROCS"); !set {
+		if cpuInfo, err := GetCgroupCPU(); err == nil {
+			numCPUToUse := int(math.Ceil(cpuInfo.CPUShares()))
+			if numCPUToUse < runtime.NumCPU() && numCPUToUse > 0 {
+				log.Infof(ctx, "running in a container; setting GOMAXPROCS to %d", numCPUToUse)
+				runtime.GOMAXPROCS(numCPUToUse)
+			}
+		}
+	}
+}