linux-kernel - Re: [PATCH 3/4] rtla/timerlat: Add example for BPF action program

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Message-ID: <321181e1e5060f0c68e0430d69e0e89688b08235.camel@redhat.com>
Date: Tue, 21 Oct 2025 12:32:01 -0500
From: Crystal Wood <crwood@...hat.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Tomas Glozar <tglozar@...hat.com>, LKML <linux-kernel@...r.kernel.org>, 
 Linux Trace Kernel <linux-trace-kernel@...r.kernel.org>, John Kacur
 <jkacur@...hat.com>, Luis Goncalves	 <lgoncalv@...hat.com>, Costa Shulyupin
 <costa.shul@...hat.com>, Wander Lairson Costa <wander@...hat.com>, Arnaldo
 Carvalho de Melo <acme@...nel.org>
Subject: Re: [PATCH 3/4] rtla/timerlat: Add example for BPF action program

On Tue, 2025-10-21 at 13:02 -0400, Steven Rostedt wrote:
> On Tue, 21 Oct 2025 10:58:06 -0500
> Crystal Wood <crwood@...hat.com> wrote:
> 
> > Huh, so I guess BPF is an exception to the "no generic printk to the
> > global trace instance except for debugging that generates a big boot
> > splat" rule?
> 
> bpf_printk() is an event and not the generic trace_printk() that would
> cause that splat. You can turn it off.

Ah, I see.

> > Speaking of which, why doesn't trace_osnoise.c call
> > trace_array_init_printk() given that it uses trace_array_printk_buf()?
> 
> Note, trace_array_printk() (which trace_array_init_printk()) only works for
> instances and does not print into the top level trace buffer.

Yes, it's for instances, such as the ones rtla creates.

-Crystal