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

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Message-ID: <aYvKqse1aXxGqFwR@google.com>
Date: Tue, 10 Feb 2026 16:17:46 -0800
From: Namhyung Kim <namhyung@...nel.org>
To: Jens Remus <jremus@...ux.ibm.com>
Cc: Steven Rostedt <rostedt@...nel.org>, 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>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>, Jiri Olsa <jolsa@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrii Nakryiko <andrii@...nel.org>,
	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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	Dylan Hatch <dylanbhatch@...gle.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
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	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

Hello,

On Mon, Feb 09, 2026 at 06:07:59PM +0100, Jens Remus wrote:
> 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).

Users (me, at least) may want to compare stacktraces from FP and SFrame?

> 
> 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"?

Sounds better.  But I think it cannot enforce "--call-graph fp,defer" to
use frame pointers when SFrame is available.. Hmm.

Thanks,
Namhyung