Re: yielding while running SCHED_DEADLINE

[Juri Lelli <juri.lelli@gmail.com>]

Hi,

On 14/09/18 23:13, Patel, Vedang wrote:
> Hi all, 
> 
> We have been playing around with SCHED_DEADLINE and found some
> discrepancy around the calculation of nr_involuntary_switches and
> nr_voluntary_switches in /proc/${PID}/sched.
> 
> Whenever the task is done with it's work earlier and executes
> sched_yield() to voluntarily gives up the CPU this increments
> nr_involuntary_switches. It should have incremented
> nr_voluntary_switches.

Mmm, I see what you are saying.

[...]

> Looking at __schedule() in kernel/sched/core.c, the switch is counted
> as part of nr_involuntary_switches if the task has not been preempted
> and the task is TASK_RUNNING state. This does not seem to happen when
> sched_yield() is called.

Mmm,

 - nr_voluntary_switches++ if !preempt && !RUNNING
 - nr_involuntary_switches++ otherwise (yield fits this as the task is
   still RUNNING, even though throttled for DEADLINE)

Not sure this is the same as what you say above..

> Is there something we are missing over here? OR Is this a known issue
> and is planned to be fixed later?

.. however, not sure. Peter, what you say. It looks like we might indeed
want to account yield as a voluntary switch, seems to fit. In this case
I guess we could use a flag or add a sched_ bit to task_struct to handle
the case?

Best,

- Juri