Re: [RESEND][PATCH v2 1/3] sched/tp: Add new tracepoint to track uclamp set from user-space

Peter Zijlstra
2023-07-06T11:15:04Z

On Wed, May 31, 2023 at 07:26:29PM +0100, Qais Yousef wrote:
> On 05/22/23 15:57, Lukasz Luba wrote:
> > The user-space can set uclamp value for a given task. It impacts task
> > placement decisions made by the scheduler. This is very useful information
> > and helps to understand the system behavior or track improvements in
> > middleware and applications which start using uclamp mechanisms and report
> > better performance in tests.
>
> Do you mind adding a generic one instead please? And explain why we can't just
> attach to the syscall via kprobes? I think you want to bypass the permission
> checks, so maybe a generic tracepoint after that might be justifiable?
> Then anyone can use it to track how userspace has changed any attributes for
> a task, not just uclamp.

Yeah, so I'm leaning towards the same, if you want to put a tracepoint
in __sched_setscheduler(), just trace the whole attr and leave it at
that:

trace_update_sched_attr_tp(p, attr);

or somesuch.