On Mon, Jul 31, 2023 at 5:37 PM Peter Zijlstra [off-list ref] wrote:

On Wed, Jul 26, 2023 at 08:16:16PM +0800, Ze Gao wrote:

quoted

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.

How about adding a new char for each distinct state you want to report
, e.g., 'F' for this for debug purposes ? I don;t think we can lose the
multiple flags just because we choose to report in chars. Still people
can use the old raw value since we do not replace but supplement it here.

Regards,
Ze