3826: Fix up CPU usage accounting.

diff --git a/services/crunchstat/crunchstat.go b/services/crunchstat/crunchstat.go
index 856eaafd88ca02c7e6e9910e72c88993ad92f441..9175cf0ba2858ba85d421cc304ffa67e5ea2658c 100644 (file)
--- a/services/crunchstat/crunchstat.go
+++ b/services/crunchstat/crunchstat.go
@@ -15,6 +15,15 @@ import (
        "time"
 )
 
+/*
+#include <unistd.h>
+#include <sys/types.h>
+#include <pwd.h>
+#include <stdlib.h>
+*/
+import "C"
+// The above block of magic allows us to look up user_hz via _SC_CLK_TCK.
+
 func CopyPipeToChan(in io.Reader, out chan string, done chan<- bool) {
        s := bufio.NewScanner(in)
        for s.Scan() {
@@ -82,6 +91,8 @@ func PollCgroupStats(cgroup_root string, cgroup_parent string, container_id stri
 
        disk := make(map[string]*Disk)
 
+       user_hz := float64(C.sysconf(C._SC_CLK_TCK))
+
        cpuacct_stat := FindStat(cgroup_root, cgroup_parent, container_id, "cpuacct", "stat")
        blkio_io_service_bytes := FindStat(cgroup_root, cgroup_parent, container_id, "blkio", "io_service_bytes")
        cpuset_cpus := FindStat(cgroup_root, cgroup_parent, container_id, "cpuset", "cpus")
@@ -118,8 +129,7 @@ func PollCgroupStats(cgroup_root string, cgroup_parent string, container_id stri
                        // Emit stats, then select again.
                }
                morning := time.Now()
-               elapsed := morning.Sub(bedtime).Nanoseconds() / int64(time.Millisecond)
-               var cpus int64 = 0
+               elapsed := morning.Sub(bedtime).Seconds()
                if cpuset_cpus != "" {
                        b, err := OpenAndReadAll(cpuset_cpus, stderr)
                        if err != nil {
@@ -127,6 +137,7 @@ func PollCgroupStats(cgroup_root string, cgroup_parent string, container_id stri
                                continue
                        }
                        sp := strings.Split(string(b), ",")
+                       cpus := int64(0)
                        for _, v := range sp {
                                var min, max int64
                                n, _ := fmt.Sscanf(v, "%d-%d", &min, &max)
@@ -136,15 +147,8 @@ func PollCgroupStats(cgroup_root string, cgroup_parent string, container_id stri
                                        cpus += 1
                                }
                        }
-
-                       if cpus != last_cpucount {
-                               stderr <- fmt.Sprintf("crunchstat: cpuset.cpus %v", cpus)
-                       }
                        last_cpucount = cpus
                }
-               if cpus == 0 {
-                       cpus = 1
-               }
                if cpuacct_stat != "" {
                        b, err := OpenAndReadAll(cpuacct_stat, stderr)
                        if err != nil {
@@ -163,19 +167,18 @@ func PollCgroupStats(cgroup_root string, cgroup_parent string, container_id stri
                        if elapsed > 0 && last_user != -1 {
                                user_diff := next_user - last_user
                                sys_diff := next_sys - last_sys
-                               // Assume we're reading stats based on 100
-                               // jiffies per second.  Because the elapsed
-                               // time is in milliseconds, we need to boost
-                               // that to 1000 jiffies per second, then boost
-                               // it by another 100x to get a percentage, then
-                               // finally divide by the actual elapsed time
-                               // and the number of cpus to get average load
-                               // over the polling period.
-                               user_pct := (user_diff * 10 * 100) / (elapsed * cpus)
-                               sys_pct := (sys_diff * 10 * 100) / (elapsed * cpus)
-
-                               stderr <- fmt.Sprintf("crunchstat: cpuacct.stat user %v", user_pct)
-                               stderr <- fmt.Sprintf("crunchstat: cpuacct.stat sys %v", sys_pct)
+                               // {*_diff} == {1/user_hz}-second
+                               // ticks of CPU core consumed in an
+                               // {elapsed}-second interval.
+                               //
+                               // We report this as CPU core usage
+                               // (i.e., 1.0 == one pegged core). We
+                               // also report the number of cores
+                               // (maximum possible usage).
+                               user := float64(user_diff) / elapsed / user_hz
+                               sys := float64(sys_diff) / elapsed / user_hz
+
+                               stderr <- fmt.Sprintf("crunchstat: cpuacct.stat user %.4f sys %.4f cpus %d interval %.4f", user, sys, last_cpucount, elapsed)
                        }
 
                        last_user = next_user