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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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