linux-kernel - Re: [PATCH v4 20/22] rv: Add rtapp

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Message-ID: <c321c7350ec10f9f358695acd765d2dbd067eeb2.camel@redhat.com>
Date: Thu, 24 Apr 2025 15:55:34 +0200
From: Gabriele Monaco <gmonaco@...hat.com>
To: Nam Cao <namcao@...utronix.de>, Steven Rostedt <rostedt@...dmis.org>, 
	linux-trace-kernel@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: john.ogness@...utronix.de
Subject: Re: [PATCH v4 20/22] rv: Add rtapp_sleep monitor

On Wed, 2025-04-23 at 08:50 +0200, Nam Cao wrote:
> Add a monitor for checking that real-time tasks do not go to sleep in
> a
> manner that may cause undesirable latency.
> 
> Also change
> 	RV depends on TRACING
> to
> 	RV select TRACING
> to avoid the following recursive dependency:
> 
>  error: recursive dependency detected!
> 	symbol TRACING is selected by PREEMPTIRQ_TRACEPOINTS
> 	symbol PREEMPTIRQ_TRACEPOINTS depends on TRACE_IRQFLAGS
> 	symbol TRACE_IRQFLAGS is selected by RV_MON_SLEEP
> 	symbol RV_MON_SLEEP depends on RV
> 	symbol RV depends on TRACING
> 
> Signed-off-by: Nam Cao <namcao@...utronix.de>
> ---
> 

I've been playing with these monitors, code-wise they look good.
I tested a bit and they seem to work without many surprises by doing
something as simple as:

perf stat -e rv:error_sleep stress-ng --cpu-sched 1 -t 10s
  -- shows several errors --

perf stat -e rv:error_sleep stress-ng --prio-inv 1 --prio-inv-policy rr
  -- shows only 1 error (normal while starting the program?) --

Not quite sound, but does it look a reasonable test to you?

I quickly tried the same with the other monitor comparing the number of
errors with the page_faults generated by perf, but that didn't make too
much sense. Perhaps I'm doing something wrong here though (the number
reported by perf for page faults feels a bit too high).

perf stat -e page-faults -e rv:error_pagefault stress-ng --cyclic 1

Anyway, the monitor looks good to me

  Reviewed-by: Gabriele Monaco <gmonaco@...hat.com>

but it'd be nice if you have tips to share how to quickly test it (e.g.
without writing a custom workload).

Thanks,
Gabriele