Re: [RFC PATCH v2 1/3] sched, tracing: add to report task state in symbolic chars

[Ze Gao <zegao2021@gmail.com>]

On Mon, Jul 31, 2023 at 5:37 PM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Wed, Jul 26, 2023 at 08:16:16PM +0800, Ze Gao wrote:
> > Internal representations of task state are likely to be changed or
> > ordered, and reporting them to userspace without exporting them as
> > part of API is not a good choice, which can easily break a userspace
> > observability tool as kernel evolves. For example, perf suffers from
> > this and still reports wrong states by this patch.
> >
> > OTOH, some masqueraded state like TASK_REPORT_IDLE and TASK_REPORT_MAX
> > are also reported inadvertently, which confuses things even more.
> >
> > So add a new variable in company with the old raw value to report task
> > state in symbolic char, which is self-explaining and no further
> > translation is needed, and also report priorities in 'short' to save
> > some buffer space.  Of course this does not break any userspace tool.
> >
> > Note for PREEMPT_ACTIVE, we introduce 'p' to report it and use the old
> > conventions for the rest.
>
> So I really dont much like this. This looses the ability to see the
> actual wait state flags, there could be multiple. Eg, things like
> TASK_FREEZEABLE gets lost completely.

Also, IIRC, TASK_FREEZABLE which is defined as 0x2000, is already lost
in the current implementation of __trace_sched_switch_state which limits
all states except PREEMPT_ACTIIVE below TASK_REPORT_IDLE to be
reported. So I do not believe you can achieve this by just leaving things alone.

Regards,
Ze