linux-kernel - Re: [PATCH v3 17/17] rv: Add opid per-cpu monitor

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Message-ID: <ecc8217af9ad8142abb73d6ef2fe9bdac9df6c95.camel@redhat.com>
Date: Wed, 16 Jul 2025 12:00:24 +0200
From: Gabriele Monaco <gmonaco@...hat.com>
To: Nam Cao <namcao@...utronix.de>
Cc: linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>, 
	linux-trace-kernel@...r.kernel.org, linux-doc@...r.kernel.org, Tomas Glozar
	 <tglozar@...hat.com>, Juri Lelli <jlelli@...hat.com>, Clark Williams
	 <williams@...hat.com>, John Kacur <jkacur@...hat.com>
Subject: Re: [PATCH v3 17/17] rv: Add opid per-cpu monitor



On Wed, 2025-07-16 at 11:38 +0200, Nam Cao wrote:
> On Tue, Jul 15, 2025 at 09:14:34AM +0200, Gabriele Monaco wrote:
> > diff --git a/kernel/trace/rv/monitors/nrp/Kconfig
> > b/kernel/trace/rv/monitors/nrp/Kconfig
> > index f37ff70e8d204..a175c430d351f 100644
> > --- a/kernel/trace/rv/monitors/nrp/Kconfig
> > +++ b/kernel/trace/rv/monitors/nrp/Kconfig
> > @@ -3,7 +3,7 @@
> >  config RV_MON_NRP
> >  	depends on RV
> >  	depends on RV_MON_SCHED
> > -	default y if !ARCH_ARM64
> > +	default y if !ARM64
> 
> I think this is not supposed to be in this patch? It has nothing to
> do with
> the opid monitor.

Damn, fixed up the wrong patch, will move it to the other one..

> 
> >  	select DA_MON_EVENTS_ID
> >  	bool "nrp monitor"
> >  	help
> > diff --git a/kernel/trace/rv/monitors/opid/Kconfig
> > b/kernel/trace/rv/monitors/opid/Kconfig
> > new file mode 100644
> > index 0000000000000..23b43d2704153
> > --- /dev/null
> > +++ b/kernel/trace/rv/monitors/opid/Kconfig
> > @@ -0,0 +1,17 @@
> > +# SPDX-License-Identifier: GPL-2.0-only
> > +#
> > +config RV_MON_OPID
> > +	depends on RV
> > +	depends on TRACE_IRQFLAGS
> > +	depends on TRACE_PREEMPT_TOGGLE
> > +	depends on RV_MON_SCHED
> > +	default y if PREEMPT_RT
> > +	select DA_MON_EVENTS_IMPLICIT
> 
> Shouldn't we add "depends on PREEMPT_RT"? I tried this monitor on
> non-RT x86 kernel, and got some errors. That could confuse people.

Mmh, my rationale was that it reports errors on non PREEMPT_RT, but it
does build. If someone wants to try it out there, they are free to do
it. We are just not supporting it officially.
The monitor might start working in the future also on non RT kernels,
or at least if someone wants to try whether it's the case, they can do
it easily.

Same idea for the ARM64 thing above.

But I should definitely mention this explicitly in the Kconfig entry
not to confuse people..

> 
> And the monitor reports some errors on riscv64 with PREEMPT_RT=y:
> 
> root@...cv:~/rv-tests# uname -a
> Linux riscv 6.16.0-rc6-00054-g7590637d9ca2 #87 SMP PREEMPT_RT Wed Jul
> 16 11:26:00 CEST 2025 riscv64 GNU/Linux
> root@...cv:~/rv-tests# stress-ng --cpu-sched -1
> stress-ng: info:  [452] defaulting to a 1 day run per stressor
> stress-ng: info:  [452] dispatching hogs: 4 cpu-sched
> [  614.390462] rv: monitor opid does not allow event irq_entry on
> state in_irq
> 

Mmh riscv.. I haven't tested it there, guess I need to start keeping a
VM somewhere.

Thanks,
Gabriele