Use cgo to get systems clock ticks for metrics

crosbymichael · crosbymichael · commit 004cf556e86a · 2014-04-21T10:26:22.000-07:00
Docker-DCO-1.1-Signed-off-by: Michael Crosby &lt;michael@crosbymichael.com&gt; (github: crosbymichael)
diff --git a/pkg/cgroups/fs/cpuacct.go b/pkg/cgroups/fs/cpuacct.go
@@ -14,7 +14,10 @@ import (
 	"github.com/dotcloud/docker/pkg/system"
 )
 
-var cpuCount = float64(runtime.NumCPU())
+var (
+	cpuCount   = float64(runtime.NumCPU())
+	clockTicks = float64(system.GetClockTicks())
+)
 
 type cpuacctGroup struct {
 }
@@ -58,7 +61,7 @@ func (s *cpuacctGroup) Stats(d *data) (map[string]float64, error) {
 		deltaSystem = lastSystem - startSystem
 	)
 	if deltaSystem > 0.0 {
-		percentage = ((deltaProc / deltaSystem) * 100.0) * cpuCount
+		percentage = ((deltaProc / deltaSystem) * clockTicks) * cpuCount
 	}
 	// NOTE: a percentage over 100% is valid for POSIX because that means the
 	// processes is using multiple cores
diff --git a/pkg/system/sysconfig.go b/pkg/system/sysconfig.go
@@ -0,0 +1,13 @@
+// +build linux,cgo
+
+package system
+
+/*
+#include <unistd.h>
+int get_hz(void) { return sysconf(_SC_CLK_TCK); }
+*/
+import "C"
+
+func GetClockTicks() int {
+	return int(C.get_hz())
+}
diff --git a/pkg/system/sysconfig_nocgo.go b/pkg/system/sysconfig_nocgo.go
@@ -0,0 +1,9 @@
+// +build linux,!cgo
+
+package system
+
+func GetClockTicks() int {
+	// when we cannot call out to C to get the sysconf it is fairly safe to
+	// just return 100
+	return 100
+}
diff --git a/pkg/system/unsupported.go b/pkg/system/unsupported.go
@@ -17,3 +17,9 @@ func UsetCloseOnExec(fd uintptr) error {
 func Gettid() int {
 	return 0
 }
+
+func GetClockTicks() int {
+	// when we cannot call out to C to get the sysconf it is fairly safe to
+	// just return 100
+	return 100
+}

Original file line number	Diff line number	Diff line change
`@@ -14,7 +14,10 @@ import (`
`14`	`14`	`"github.com/dotcloud/docker/pkg/system"`
`15`	`15`	`)`
`16`	`16`
`17`		`-var cpuCount = float64(runtime.NumCPU())`
	`17`	`+var (`
	`18`	`+ cpuCount = float64(runtime.NumCPU())`
	`19`	`+ clockTicks = float64(system.GetClockTicks())`
	`20`	`+)`
`18`	`21`
`19`	`22`	`type cpuacctGroup struct {`
`20`	`23`	`}`
`@@ -58,7 +61,7 @@ func (s cpuacctGroup) Stats(d data) (map[string]float64, error) {`
`58`	`61`	`deltaSystem = lastSystem - startSystem`
`59`	`62`	`)`
`60`	`63`	`if deltaSystem > 0.0 {`
`61`		`- percentage = ((deltaProc / deltaSystem) * 100.0) * cpuCount`
	`64`	`+ percentage = ((deltaProc / deltaSystem) * clockTicks) * cpuCount`
`62`	`65`	`}`
`63`	`66`	`// NOTE: a percentage over 100% is valid for POSIX because that means the`
`64`	`67`	`// processes is using multiple cores`