Leave minimum CPU number as a constant

Remove introduced CPUNumMin config and hard-code it as 2.

runsc/boot/config.go

@@ -256,12 +256,6 @@ type Config struct {
 	//
 	// E.g. 0.2 CPU quota will result in 1, and 1.9 in 2.
 	CPUNumFromQuota bool
-
-	// CPUNumMin is minimum value of CPU number setting when CPUNumFromQuota
-	// strategy is active.
-	//
-	// E.g. when CPUNumMin is 2, 0.2 CPU quota will result in 2 instead of 1.
-	CPUNumMin int
 }
 
 // ToFlags returns a slice of flags that correspond to the given Config.
@@ -295,9 +289,7 @@ func (c *Config) ToFlags() []string {
 		"--overlayfs-stale-read=" + strconv.FormatBool(c.OverlayfsStaleRead),
 	}
 	if c.CPUNumFromQuota {
-		f = append(f, "--cpu-num-from-quota",
-			"--cpu-num-min="+strconv.Itoa(c.CPUNumMin),
-		)
+		f = append(f, "--cpu-num-from-quota")
 	}
 	// Only include these if set since it is never to be used by users.
 	if c.TestOnlyAllowRunAsCurrentUserWithoutChroot {

runsc/main.go

@@ -82,8 +82,7 @@ var (
 	numNetworkChannels = flag.Int("num-network-channels", 1, "number of underlying channels(FDs) to use for network link endpoints.")
 	rootless           = flag.Bool("rootless", false, "it allows the sandbox to be started with a user that is not root. Sandbox and Gofer processes may run with same privileges as current user.")
 	referenceLeakMode  = flag.String("ref-leak-mode", "disabled", "sets reference leak check mode: disabled (default), log-names, log-traces.")
-	cpuNumFromQuota    = flag.Bool("cpu-num-from-quota", false, "set cpu number to cpu quota (least integer greater or equal to quota value)")
-	cpuNumMin          = flag.Int("cpu-num-min", 2, "minimum number of cpu to use with --cpu-num-from-quota")
+	cpuNumFromQuota    = flag.Bool("cpu-num-from-quota", false, "set cpu number to cpu quota (least integer greater or equal to quota value, but not less than 2)")
 
 	// Test flags, not to be used outside tests, ever.
 	testOnlyAllowRunAsCurrentUserWithoutChroot = flag.Bool("TESTONLY-unsafe-nonroot", false, "TEST ONLY; do not ever use! This skips many security measures that isolate the host from the sandbox.")
@@ -228,7 +227,6 @@ func main() {
 		ReferenceLeakMode:  refsLeakMode,
 		OverlayfsStaleRead: *overlayfsStaleRead,
 		CPUNumFromQuota:    *cpuNumFromQuota,
-		CPUNumMin:          *cpuNumMin,
 
 		TestOnlyAllowRunAsCurrentUserWithoutChroot: *testOnlyAllowRunAsCurrentUserWithoutChroot,
 		TestOnlyTestNameEnv:                        *testOnlyTestNameEnv,

runsc/sandbox/sandbox.go

@@ -633,13 +633,18 @@ func (s *Sandbox) createSandboxProcess(conf *boot.Config, args *Args, startSyncF
 			return fmt.Errorf("getting cpu count from cgroups: %v", err)
 		}
 		if conf.CPUNumFromQuota {
+			// Dropping below 2 CPUs can trigger application to disable
+			// locks that can lead do hard to debug errors, so just
+			// leaving two cores as reasonable default.
+			const minCPUs = 2
+
 			quota, err := s.Cgroup.CPUQuota()
 			if err != nil {
 				return fmt.Errorf("getting cpu qouta from cgroups: %v", err)
 			}
 			if n := int(math.Ceil(quota)); n > 0 {
-				if n < conf.CPUNumMin {
-					n = conf.CPUNumMin
+				if n < minCPUs {
+					n = minCPUs
 				}
 				if n < cpuNum {
 					// Only lower the cpu number.