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    SubjectRe: [PATCH 8/9] per-cgroup boot time
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    On Wed, 2011-09-14 at 17:04 -0300, Glauber Costa wrote:
    > 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);


    I'm confused, what does it do? You take a boot time timestamp at cgroup
    creation, add that to all boot-time readings and print the result. How
    does that make sense? Subtracting the start_time, maybe, that would make
    the cgroup creation time 0, adding, not so much.


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