[PATCH 8/9] per-cgroup boot time

[Glauber Costa <glommer@parallels.com>]

Record the time in which the cgroup was created. This can be
used to provide a more accurate boottime information in
cpuacct.proc.stat.

Signed-off-by: Glauber Costa <glommer@parallels.com>
---
 kernel/sched.c |    8 +++++++-
 1 files changed, 7 insertions(+), 1 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index 4611c54..8f254d0 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -9120,6 +9120,7 @@ struct cpuacct {
 	/* cpuusage holds pointer to a u64-type object on every cpu */
 	u64 __percpu *cpuusage;
 	u64 __percpu *cpustat;
+	struct timespec start_time;
 };
 
 struct cgroup_subsys cpuacct_subsys;
@@ -9172,6 +9173,8 @@ static struct cgroup_subsys_state *cpuacct_create(
 		acct[CPUACCT_STAT_IDLE] = kstat_cpu(i).cpustat.idle;
 		acct[CPUACCT_STAT_IOWAIT] = kstat_cpu(i).cpustat.iowait;
 	}
+
+	get_monotonic_boottime(&ca->start_time);
 	return &ca->css;
 
 out_free_usage:
@@ -9316,13 +9319,16 @@ static int cpuacct_proc_stat(struct cgroup *cgrp, struct cftype *cft,
 	unsigned int per_softirq_sums[NR_SOFTIRQS] = {0};
 	struct timespec boottime;
 	struct cpuacct *ca = cgroup_ca(cgrp);
+	struct timespec ts;
 	u64 *cpustat;
 
 	user = nice = system = idle = iowait =
 		irq = softirq = steal = cputime64_zero;
 	guest = guest_nice = cputime64_zero;
 	getboottime(&boottime);
-	jif = boottime.tv_sec;
+	getboottime(&boottime);
+	ts = timespec_add(boottime, ca->start_time);
+	jif = ts.tv_sec;
 
 	for_each_possible_cpu(i) {
 		cpustat = per_cpu_ptr(ca->cpustat, i);
-- 
1.7.6