Re: [PATCH 8/9] per-cgroup boot time

[Glauber Costa]

On 09/20/2011 06:25 AM, Peter Zijlstra wrote:
> 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@xxxxxxxxxxxxx>
> > ---
> >   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.

Boot time represent at which times the machine was booted. In this 
context, at which time the container/cgroup was created. So it have to 
be an addition.... don't really understand your question
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