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Message-ID: <20231016110312.3d18ea82@gandalf.local.home>
Date: Mon, 16 Oct 2023 11:03:12 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Daniel Vetter <daniel@...ll.ch>
Cc: Pekka Paalanen <ppaalanen@...il.com>, jim.cromie@...il.com,
Ćukasz Bartosik <lb@...ihalf.com>,
linux-kernel@...r.kernel.org,
"wayland-devel@...ts.freedesktop.org"
<wayland-devel@...ts.freedesktop.org>,
Sean Paul <seanpaul@...omium.org>,
dri-devel <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH v1] dynamic_debug: add support for logs destination
On Thu, 12 Oct 2023 11:53:52 +0200
Daniel Vetter <daniel@...ll.ch> wrote:
> > You said that turning the kernel ring buffer contents into strings is a
> > very heavy operation, so it is not possible to push this scope
> > separation to userspace, right?
>
> I think it's the kernel that does the formatting, but honestly not sure
> how this works with perf traces. Might be that it's actually userspace
> doing the formatting later on so that it doesn't incur the overhead while
> recording.
perf and trace-cmd do the formatting in user space via libtraceevent:
git://git.kernel.org/pub/scm/libs/libtrace/libtraceevent.git
It reads the format files of the events:
/sys/kernel/tracing/events/*/*/format
and uses that to read the raw data saved from the kernel into human
readable output.
Note, this means that addresses coming from kernel trace events are not
hashed!
-- Steve
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