linux-kernel - Re: [RFC PATCH 03/86] Revert "ftrace: Use preemption model accessors for trace header printout"

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Message-ID: <877cmtywpy.fsf@oracle.com>
Date:   Tue, 07 Nov 2023 15:23:05 -0800
From:   Ankur Arora <ankur.a.arora@...cle.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Ankur Arora <ankur.a.arora@...cle.com>,
        linux-kernel@...r.kernel.org, tglx@...utronix.de,
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Subject: Re: [RFC PATCH 03/86] Revert "ftrace: Use preemption model
 accessors for trace header printout"


Steven Rostedt <rostedt@...dmis.org> writes:

> On Tue,  7 Nov 2023 13:56:49 -0800
> Ankur Arora <ankur.a.arora@...cle.com> wrote:
>
>> This reverts commit 089c02ae2771a14af2928c59c56abfb9b885a8d7.
>
> I rather not revert this.
>
> If user space can decided between various version of preemption, then the
> trace should reflect that. At least state what the preemption model was when
> a trace started, or currently is.
>
Oh absolutely. As I mention in the cover at least these three patches
would be back:

       089c02ae2771 ("ftrace: Use preemption model accessors for trace header printout")
       cfe43f478b79 ("preempt/dynamic: Introduce preemption model accessors")
       5693fa74f98a ("kcsan: Use preemption model accessors")

The intent was (which I didn't do for the RFC), to do the reverts as cleanly
as possible, do the changes for the series and then bring these patches back
with appropriate modifications.

> That is, the model may not be "static" per boot. Anyway, the real change here should be:

Yeah, I intended to do something like that.

Or would you prefer these not be reverted (and reapplied) at all -- just fixed
as you describe here?

> Then this way we can decided to make it runtime dynamic, we don't need to
> fiddle with the tracing code again.

Yeah, that makes sense.

--
ankur