Re: Kernelshark: funcgraph_exit events don't seem to exit?

From: Yordan Karadzhov <y.karadz@gmail.com>
To: Matteo Bertolino <matteo.bertolino@huawei.com>,
	"linux-trace-users@vger.kernel.org" 
	<linux-trace-users@vger.kernel.org>
Subject: Re: Kernelshark: funcgraph_exit events don't seem to exit?
Date: Thu, 8 Sep 2022 22:04:19 +0300	[thread overview]
Message-ID: <24b50f34-b1ab-27d5-9c31-89a95d3d9fb5@gmail.com> (raw)
In-Reply-To: <134054c70c58468383174c1f62179fc3@huawei.com>

Hi Matteo,

On 9/7/22 11:08, Matteo Bertolino wrote:
> If that doesn't annoy you too much, may you give me some hints about writing a Kernelshark's plugin?

As I already mentioned, we have a plugin for sched events, so you can 
use this plugin as starting point, despite that your plugin will be by 
far simpler.

Have a look here
https://git.kernel.org/pub/scm/utils/trace-cmd/kernel-shark.git/tree/src/plugins/sched_events.h

and here
https://git.kernel.org/pub/scm/utils/trace-cmd/kernel-shark.git/tree/src/plugins/sched_events.c

and see how you can define a context object for your plugin and how you 
can register a plugin action that will be executed over each entry in 
the data that is event of a given type. Example of such action for 
sched_switch events:
https://git.kernel.org/pub/scm/utils/trace-cmd/kernel-shark.git/tree/src/plugins/sched_events.c#n102

As a first step, try to register a plugin action for the 
'funcgraph_exit' event that will set the 'pid' of the entry to 'idle'

entry->pid = stream->idle_pid

This will be enough to have half of the work done.

You can build your plugin, using the 'BUILD_PLUGIN' macro here:
https://git.kernel.org/pub/scm/utils/trace-cmd/kernel-shark.git/tree/src/plugins/CMakeLists.txt

Let me know when you are ready with this and we will figure out how to 
implement the other features that you want.

cheers,
Yordan