From: Steven Rostedt <rostedt@goodmis•org>
To: Bert Karwatzki <spasswolf@web•de>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix•de>,
linux-kernel@vger•kernel.org, linux-next@vger•kernel.org,
bpf@vger•kernel.org, linux-rt-users@vger•kernel.org,
linux-rt-devel@lists•linux.dev,
Thomas Gleixner <tglx@linutronix•de>,
Alexei Starovoitov <alexei.starovoitov@gmail•com>
Subject: Re: BUG: scheduling while atomic with PREEMPT_RT=y and bpf selftests
Date: Fri, 6 Jun 2025 09:57:12 -0400 [thread overview]
Message-ID: <20250606095712.7287fa31@gandalf.local.home> (raw)
In-Reply-To: <b86bd98b23d1299981c4e95b593eb5a144fbf822.camel@web.de>
On Fri, 06 Jun 2025 15:13:05 +0200
Bert Karwatzki <spasswolf@web•de> wrote:
> I tried this and first thought my kernel did not have the right configuration as
>
> # trace-cmd record -e preempt_disable -e preempt_enable
>
> seemed to do nothing in particular, but it turns out it takes a long time to start
> (~1min) when the kernel is compiled with CONFIG_LOCKDEP=y. (on the standard debian
Yeah, that's a recent regression in the code which I'm currently testing a
fix for:
https://lore.kernel.org/linux-trace-kernel/20250605161701.35f7989a@gandalf.local.home
> kernel starting to record takes less time, but it does not have CONFIG_PREEMPT_TRACER.)
>
> So after the trace-cmd was running I ran the bpf example and got a trace.dat:
>
> # ls -lh trace.dat
> -rw-r--r-- 1 root root 152M 6. Jun 14:41 trace.dat
>
> turning this into a report with
>
> # trace-cmd report > preemp_trace.rep
>
> gives a rather unwieldly large file
Of course, it's recording every time preemption is enabled and disabled ;-)
I usually run it with a test:
# trace-cmd record -e preempt_disable -e preempt_enable ./myprog
Where it will stop when ./myprog is done.
>
> # ls -lh preempt_trace.rep
> -rw-rw-r-- 1 root root 7,4G 6. Jun 14:46 preempt_trace.rep
>
> This file has about 61 million lines
>
> # wc -l preempt_trace.rep
> 61627360 preempt_trace.rep
>
> but only 742104 corresponding to the bpf example program "test_progs"
>
> # grep test_progs preempt_trace.rep | wc -l
> 742104
# trace-cmd record -e preempt_disable -e preempt_enable -F ./test_progs
where "-F" means "follow" and will only record when "./test_progs" is running.
Add "-c" to also trace its children.
>
> Is it possible to filter the preempt_{en,dis}able events by task name (i.e.
> get_current()->comm)?
>
> I tried this (from https://code.tools/man/1/trace-cmd-report/) but it
> fails with an error message:
> # trace-cmd record -e preempt_enable -F '.*:COMM == "test_progs"' -e preempt_disable -F '.*:COMM == "test_progs"'
-F means to execute. The -F in trace-cmd report is filter (that's because
-f was already taken :-p)
-- Steve
>
> ********************
> Unable to exec .*:COMM == "test_progs"
> ********************
> trace-cmd: No such file or directory
> Failed to exec .*:COMM == "test_progs"
> libtracecmd: No such file or directory
> can not stat 'trace.dat.cpu0'
>
>
> Bert Karwatzki
next prev parent reply other threads:[~2025-06-06 13:56 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-06-05 9:19 BUG: scheduling while atomic with PREEMPT_RT=y and bpf selftests Bert Karwatzki
2025-06-05 12:48 ` Steven Rostedt
2025-06-05 12:51 ` Sebastian Andrzej Siewior
2025-06-08 8:45 ` Bert Karwatzki
2025-06-08 15:53 ` Bert Karwatzki
2025-06-09 11:37 ` Bert Karwatzki
2025-06-14 12:01 ` Bert Karwatzki
2025-06-15 22:12 ` Bert Karwatzki
2025-06-16 6:28 ` Sebastian Andrzej Siewior
2025-06-06 13:13 ` Bert Karwatzki
2025-06-06 13:57 ` Steven Rostedt [this message]
-- strict thread matches above, loose matches on Subject: below --
2025-05-25 22:47 Bert Karwatzki
2025-05-26 1:32 ` Alexei Starovoitov
2025-05-26 9:22 ` Bert Karwatzki
2025-05-27 7:19 ` Sebastian Andrzej Siewior
2025-05-25 12:14 Bert Karwatzki
2025-05-25 11:54 Bert Karwatzki
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