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

[Masami Hiramatsu (Google) <mhiramat@kernel.org>]

On Wed, 31 May 2023 19:26:29 +0100
Qais Yousef <qyousef@layalina.io> 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?

Could you tell me more about this point? I would like to know what kind of
permission checks can be bypassed with tracepoints.

> Then anyone can use it to track how userspace has changed any attributes for
> a task, not just uclamp.

I guess Uclamp is not controlled by syscall but from kernel internal
sched_setattr/setscheduler() too. Anyway I agree that it can be more generic
tracepoint, something like trace_sched_set_scheduer(task, attr).

Thank you,

> 
> 
> Thanks
> 
> --
> Qais Yousef
> 
> > 
> > Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
> > ---
> >  include/trace/events/sched.h | 4 ++++
> >  kernel/sched/core.c          | 5 +++++
> >  2 files changed, 9 insertions(+)
> > 
> > diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
> > index fbb99a61f714..dbfb30809f15 100644
> > --- a/include/trace/events/sched.h
> > +++ b/include/trace/events/sched.h
> > @@ -735,6 +735,10 @@ DECLARE_TRACE(sched_update_nr_running_tp,
> >  	TP_PROTO(struct rq *rq, int change),
> >  	TP_ARGS(rq, change));
> >  
> > +DECLARE_TRACE(uclamp_update_tsk_tp,
> > +	TP_PROTO(struct task_struct *tsk, int uclamp_id,  unsigned int value),
> > +	TP_ARGS(tsk, uclamp_id, value));
> > +
> >  #endif /* _TRACE_SCHED_H */
> >  
> >  /* This part must be outside protection */
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index 944c3ae39861..7b9b800ebb6c 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -114,6 +114,7 @@ EXPORT_TRACEPOINT_SYMBOL_GPL(sched_overutilized_tp);
> >  EXPORT_TRACEPOINT_SYMBOL_GPL(sched_util_est_cfs_tp);
> >  EXPORT_TRACEPOINT_SYMBOL_GPL(sched_util_est_se_tp);
> >  EXPORT_TRACEPOINT_SYMBOL_GPL(sched_update_nr_running_tp);
> > +EXPORT_TRACEPOINT_SYMBOL_GPL(uclamp_update_tsk_tp);
> >  
> >  DEFINE_PER_CPU_SHARED_ALIGNED(struct rq, runqueues);
> >  
> > @@ -1956,12 +1957,16 @@ static void __setscheduler_uclamp(struct task_struct *p,
> >  	    attr->sched_util_min != -1) {
> >  		uclamp_se_set(&p->uclamp_req[UCLAMP_MIN],
> >  			      attr->sched_util_min, true);
> > +		trace_uclamp_update_tsk_tp(p, UCLAMP_MIN,
> > +					   attr->sched_util_min);
> >  	}
> >  
> >  	if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MAX &&
> >  	    attr->sched_util_max != -1) {
> >  		uclamp_se_set(&p->uclamp_req[UCLAMP_MAX],
> >  			      attr->sched_util_max, true);
> > +		trace_uclamp_update_tsk_tp(p, UCLAMP_MAX,
> > +					   attr->sched_util_max);
> >  	}
> >  }
> >  
> > -- 
> > 2.25.1
> > 


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>