On Fri, Apr 08, 2022 at 01:45:35PM +0100, Matthew Wilcox wrote:
> On Fri, Apr 08, 2022 at 05:31:06PM +0800, brookxu.cn wrote:
> > From: Chunguang Xu <brookxu@xxxxxxxxxxx>
> >
> > In the current implementation, cpu_time and rq_time should be
> > in nanoseconds, so this document needs to be modified.
>
> I agree that this is wrong, but we shouldn't be changing the units
> of measurement reported to userspace without changing the schedstats
> version. I suspect this was an inadvertent change, and we should be
> converting from sched_clock() time (~= ns) to jiffies in show_schedstat().
> Adding scheduler experts.
Seems to have happend at 425e0968a25f ("sched: move code into
kernel/sched_stats.h").
Before that we have:
-static inline void
-rq_sched_info_depart(struct rq *rq, unsigned long delta_jiffies)
-{
- if (rq)
- rq->rq_sched_info.cpu_time += delta_jiffies;
-}
-static inline void sched_info_depart(struct task_struct *t)
-{
- unsigned long delta_jiffies = jiffies - t->sched_info.last_arrival;
-
- t->sched_info.cpu_time += delta_jiffies;
- rq_sched_info_depart(task_rq(t), delta_jiffies);
-}
afterwards we have:
+static inline void sched_info_depart(struct task_struct *t)
+{
+ unsigned long long delta = sched_clock() - t->sched_info.last_arrival;
+
+ t->sched_info.cpu_time += delta;
+ rq_sched_info_depart(task_rq(t), delta);
+}
And that's 15 years and at least one SCHEDSTAT_VERSION ago (although
this change itself didn't bump the version).
So I'm thinking we can update the documentation and forget about this.
