linux-kernel - Re: Interface for enabling context tracking

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Message-ID: <20250417163436.599e50a1@gandalf.local.home>
Date: Thu, 17 Apr 2025 16:34:36 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Junxuan Liao <ljx@...wisc.edu>
Cc: Frederic Weisbecker <frederic@...nel.org>, "Paul E. McKenney"
 <paulmck@...nel.org>, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org, Masami Hiramatsu <mhiramat@...nel.org>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: Re: Interface for enabling context tracking

On Thu, 17 Apr 2025 14:10:53 -0500
Junxuan Liao <ljx@...wisc.edu> wrote:

> Just found out that the exit tracepoints for syscalls aren't always
> exactly preceding the exit to userspace. The kernel can still spend
> quite some time in task_work_run after the tracepoints are triggered.
> Has that bothered you before?

It's been a while, but what I usually do when I want to see entry into the
kernel is also to run:

  trace-cmd set -p function_graph --max-graph-depth 1

Which tracks the first function call into the kernel. It obviously now
misses entry and exit from user mode due to noinstr, but if a task_work
function is called, it will usually catch that too.

-- Steve