linux-kernel - Re: [PATCH v13 00/18] unwind_deferred: Implement sframe handling

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Message-ID: <113e4e4d-8b7a-437d-a3a2-de74acc9ecaa@linux.ibm.com>
Date: Mon, 9 Feb 2026 18:07:59 +0100
From: Jens Remus <jremus@...ux.ibm.com>
To: Steven Rostedt <rostedt@...nel.org>, Namhyung Kim <namhyung@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        bpf@...r.kernel.org, x86@...nel.org, linux-mm@...ck.org,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Masami Hiramatsu
 <mhiramat@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
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        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
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        Indu Bhagat <indu.bhagat@...cle.com>,
        "Jose E. Marchesi" <jemarch@....org>,
        Beau Belgrave <beaub@...ux.microsoft.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Florian Weimer <fweimer@...hat.com>, Kees Cook <kees@...nel.org>,
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 <mhocko@...e.com>, Mike Rapoport <rppt@...nel.org>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>, Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>
Subject: Re: [PATCH v13 00/18] unwind_deferred: Implement sframe handling

On 2/5/2026 7:54 PM, Steven Rostedt wrote:
> On Thu, 5 Feb 2026 10:26:10 -0800
> Namhyung Kim <namhyung@...nel.org> wrote:
> 
>>> Namhyung Kim's related perf tools deferred callchain support can be used
>>> for testing ("perf record --call-graph fp,defer" and "perf report/script").  
>>
>> Is it possible for users to choose the unwinder - frame pointer or
>> SFrame at runtime?  I feel like the option should be
>> "--call-graph sframe,defer" or just "--call-graph sframe" if it always
>> uses deferred unwinding.
> 
> Currently no, and I'm not sure we want that do we? The idea is to use the
> best option that is available. Why use frame pointers if sframe is
> available and it's being called with defer?
> 
> If there's no defer, then sframes are not available, so it defaults to the
> best option available (which will likely be frame pointers).

Maybe it would make sense not to "overload" the perf record option
"--call-graph fp,defer" and use it for all deferred unwinding methods.

What about "--call-graph defer", "--call-graph any,defer", or
"--call-graph *,defer"?

Regards,
Jens
-- 
Jens Remus
Linux on Z Development (D3303)
jremus@...ibm.com / jremus@...ux.ibm.com

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