Re: [RFC][PATCH v2 1/7] taskstats: Add new taskstats commandTASKSTATS_CMD_ATTR_PIDS

[Michael Holzheu]

Hello Peter,

On Sat, 2010-11-13 at 20:20 +0100, Peter Zijlstra wrote:
> On Thu, 2010-11-11 at 18:03 +0100, Michael Holzheu wrote:
> > As clock for 'now' and 'time' the sched_clock() function is used and the patch
> 
> > +       preempt_disable();
> > +       stats->time_ns = sched_clock();
> > +       preempt_enable();
> 
> > +       task_snap_time = sched_clock();
> 
> That's just plain broken...

What exactly do you mean? Do you mean that we should not use
sched_clock() in general or that it is called twice?

> 
> 
> > +       t->sched_info.last_depart = task_rq(t)->clock;
> 
> Are you sure you don't mean task_rq(t)->clock_task ?

Maybe... I want to save in "last_depart" a sched_clock() timestamp that
is as precise as possible.

We use "last_depart" for the TASKSTATS_CMD_ATTR_PIDS command to find out
which tasks have been running on a CPU since the last taskstats
snapshot. We return all tasks where last_depart > MIN(stats->time_ns for
all tasks of last snapshot).

Michael



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