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Date: Thu, 25 Dec 2008 09:24:56 +0100 From: Ingo Molnar <mingo@...e.hu> To: Hidetoshi Seto <seto.hidetoshi@...fujitsu.com> Cc: linux-kernel@...r.kernel.org Subject: Re: [PATCH] posix-cpu-timers: clock_gettime(CLOCK_THREAD_CPUTIME_ID) goes backward * Hidetoshi Seto <seto.hidetoshi@...fujitsu.com> wrote: > --- a/kernel/sched.c > +++ b/kernel/sched.c > @@ -4064,6 +4064,33 @@ DEFINE_PER_CPU(struct kernel_stat, kstat); > EXPORT_PER_CPU_SYMBOL(kstat); > > /* > + * Return total of runtime which already banked and which not yet > + * @p in case that task is currently running. > + */ > +unsigned long long task_total_exec(struct task_struct *p) > +{ > + unsigned long flags; > + struct rq *rq; > + u64 ns = 0; > + > + rq = task_rq_lock(p, &flags); > + > + if (task_current(rq, p)) { > + u64 delta_exec; > + > + update_rq_clock(rq); > + delta_exec = rq->clock - p->se.exec_start; > + if ((s64)delta_exec > 0) > + ns = delta_exec; > + } > + ns += p->se.sum_exec_runtime; > + > + task_rq_unlock(rq, &flags); > + > + return ns; > +} > + ok - the issue is real, but there's a few implementational details. Did you know about task_delta_exec()? This new function duplicates that function's behavior - and task_delta_exec() is already used by posix task/cpu timers. I find your new task_total_exec() interface better (it's easier to use), could you have a look at eliminating task_delta_exec() users and migrating them over to task_total_exec()? Maybe even change the name of sum_exec_runtime over to __sum_exec_runtime, to make sure nobody uses the 'raw' value - which is always stale up to one tick's worth of execution. Accessing that raw value would only make sense after the task has finished executing. (i.e. at cutime/cstime collection time) Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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