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    SubjectRe: [PATCH] posix-cpu-timers: clock_gettime(CLOCK_*_CPUTIME_ID) goes backward
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    On Fri, 2008-12-26 at 09:43 +0100, Ingo Molnar wrote:
    > * Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com> wrote:
    >
    > > @@ -321,7 +287,7 @@ static int cpu_clock_sample_group(const clockid_t which_clock,
    > > cpu->cpu = cputime.utime;
    > > break;
    > > case CPUCLOCK_SCHED:
    > > - cpu->sched = cputime.sum_exec_runtime + task_delta_exec(p);
    > > + cpu->sched = cputime.sum_exec_runtime;
    > > break;
    > > }
    >
    > hm, doesnt this regress precision?

    No, he folds it into:

    > +void thread_group_cputime(struct task_struct *p, struct task_cputime *times)
    > +{
    > + unsigned long flags;
    > + struct rq *rq;
    > + u64 delta_exec = 0;
    > + struct task_cputime *tot;
    > + struct signal_struct *sig;
    > + int i;
    > +
    > + sig = p->signal;
    > + if (unlikely(!sig) || !sig->cputime.totals) {
    > + times->utime = p->utime;
    > + times->stime = p->stime;
    > + times->sum_exec_runtime = task_total_exec(p);
    > + return;
    > + }
    > +
    > + times->stime = times->utime = cputime_zero;
    > + times->sum_exec_runtime = 0;
    > +
    > + rq = task_rq_lock(p, &flags);
    > +
    > + if (task_current(rq, p)) {
    > + update_rq_clock(rq);
    > + delta_exec = rq->clock - p->se.exec_start;
    > + if ((s64)delta_exec < 0)
    > + delta_exec = 0;
    > + }
    > +
    > + for_each_possible_cpu(i) {
    > + tot = per_cpu_ptr(p->signal->cputime.totals, i);
    > + times->utime = cputime_add(times->utime, tot->utime);
    > + times->stime = cputime_add(times->stime, tot->stime);
    > + times->sum_exec_runtime += tot->sum_exec_runtime;
    > + }
    > + times->sum_exec_runtime += delta_exec;
    > +
    > + task_rq_unlock(rq, &flags);
    > +}

    Which reminds me, why do we still have this crap in the kernel? I
    thought we pretty much showed the per-cpu itimer thing was utter crap?
    -- can we pretty please either revert that or apply
    http://lkml.org/lkml/2008/11/24/183 ?

    Also, I really don't like the above, we now do the per-cpu loop with the
    RQ lock held...



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