From ded58db1ebddcfd7669a39d5158cd3aa3258c6bf Mon Sep 17 00:00:00 2001
From: Michael Crosby <michael@crosbymichael.com>
Date: Mon, 21 Apr 2014 10:26:03 -0700
Subject: [PATCH] Use cgo to get systems clock ticks for metrics
 Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com>
 (github: crosbymichael)

---
 cgroups/fs/cpuacct.go     |  7 +++++--
 system/sysconfig.go       | 13 +++++++++++++
 system/sysconfig_nocgo.go |  9 +++++++++
 system/unsupported.go     |  6 ++++++
 4 files changed, 33 insertions(+), 2 deletions(-)
 create mode 100644 system/sysconfig.go
 create mode 100644 system/sysconfig_nocgo.go

diff --git a/cgroups/fs/cpuacct.go b/cgroups/fs/cpuacct.go
index 8c123b7..4ea2b1f 100644
--- a/cgroups/fs/cpuacct.go
+++ b/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/system/sysconfig.go b/system/sysconfig.go
new file mode 100644
index 0000000..dcbe6c9
--- /dev/null
+++ b/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/system/sysconfig_nocgo.go b/system/sysconfig_nocgo.go
new file mode 100644
index 0000000..7ca3488
--- /dev/null
+++ b/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/system/unsupported.go b/system/unsupported.go
index c52a1e5..4ae2a48 100644
--- a/system/unsupported.go
+++ b/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
+}