linux-kernel - Re: [PATCH v11 00/14] unwind_user: x86: Deferred unwinding infrastructure

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Message-ID: <87wm8qlsuk.fsf@gentoo.org>
Date: Wed, 02 Jul 2025 12:44:51 +0100
From: Sam James <sam@...too.org>
To: fweimer@...hat.com
Cc: akpm@...ux-foundation.org,andrii@...nel.org,axboe@...nel.dk,beaub@...ux.microsoft.com,bpf@...r.kernel.org,indu.bhagat@...cle.com,jemarch@....org,jolsa@...nel.org,jpoimboe@...nel.org,jremus@...ux.ibm.com,linux-kernel@...r.kernel.org,linux-trace-kernel@...r.kernel.org,mathieu.desnoyers@...icios.com,mhiramat@...nel.org,mingo@...nel.org,namhyung@...nel.org,peterz@...radead.org,rostedt@...dmis.org,tglx@...utronix.de,torvalds@...ux-foundation.org,x86@...nel.org
Subject: Re: [PATCH v11 00/14] unwind_user: x86: Deferred unwinding
 infrastructure

I started to play around with this properly last night and it was
straightforward, fortunately.

Did initially attempt to backport to 6.15 but it was a victim of some
mm refactoring and didn't seem worth to carry on w/ that route.

Started a rough page with notes for myself (but corrections & such
welcome) at https://wiki.gentoo.org/wiki/Project:Toolchain/SFrame but
honestly, it's immediately obvious (and beautiful) when it's working
correctly. I've used Namhyung Kim's example from this thread but you can
see it easily with `perf top -g` too.

In one of the commit messages in the perf series, Steven also gave `perf
record -g -vv true` which was convenient for making sure it's correctly
discovered deferred unwinding support.

I plan on doing measurements next and doing some more playing once I've
built more userland with it.