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

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Message-ID: <CAP4=nvQGM_L3dpVpb36umrwZiCT+S4kGQOfENHBXRRNcy0MA8g@mail.gmail.com>
Date: Thu, 23 Oct 2025 09:27:08 +0200
From: Tomas Glozar <tglozar@...hat.com>
To: Crystal Wood <crwood@...hat.com>
Cc: Steven Rostedt <rostedt@...dmis.org>, 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

út 21. 10. 2025 v 19:32 odesílatel Crystal Wood <crwood@...hat.com> napsal:
>
> On Tue, 2025-10-21 at 13:02 -0400, Steven Rostedt wrote:
> >
> > 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
>

Right, it actually works with the trace instance, when set up properly:

[root@cs9 rtla]# ./rtla timerlat hist -T 1 -c 0 -e
bpf_trace:bpf_trace_printk --on-end trace --on-end shell,command='grep
bpf_trace_printk timerlat_trace.txt' --bpf-action
example/timerlat_bpf_action.o
# RTLA timerlat histogram
# Time unit is microseconds (us)
# Duration:   0 00:00:01
Index   IRQ-000   Thr-000   Usr-000
6             1         0         0
21            0         1         0
over:         0         0         0
count:        1         1         0
min:          6        21         -
avg:          6        21         -
max:          6        21         -
ALL:        IRQ       Thr       Usr
count:        1         1         0
min:          6        21         -
avg:          6        21         -
max:          6        21         -
 Saving trace to timerlat_trace.txt
    timerlatu/0-47791   [000] ...22 863353.286497: bpf_trace_printk:
Latency: 21282

Tomas