linux-kernel - Re: [PATCH v13 00/11] perf: Support the deferred unwinding infrastructure

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Message-ID: <20250711165654.08ab1dc5@gandalf.local.home>
Date: Fri, 11 Jul 2025 16:56:54 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Steven Rostedt <rostedt@...nel.org>, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org, bpf@...r.kernel.org, x86@...nel.org,
 Masami Hiramatsu <mhiramat@...nel.org>, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>, Josh Poimboeuf <jpoimboe@...nel.org>,
 Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...nel.org>, Jiri
 Olsa <jolsa@...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>,
 Jens Remus <jremus@...ux.ibm.com>, Linus Torvalds
 <torvalds@...ux-foundation.org>, Andrew Morton <akpm@...ux-foundation.org>,
 Jens Axboe <axboe@...nel.dk>, Florian Weimer <fweimer@...hat.com>, Sam
 James <sam@...too.org>
Subject: Re: [PATCH v13 00/11] perf: Support the deferred unwinding
 infrastructure

On Fri, 11 Jul 2025 13:26:28 -0700
Namhyung Kim <namhyung@...nel.org> wrote:

> > - Removed use of timestamp. The deferred unwind has gone back to using
> >   cookies, and perf doesn't use the cookie. This means the
> >   struct perf_callchain_deferred_event is not modified.  
> 
> What about adding the cookies in the records to handle lost data?  Even
> if it's not necessary to match callchains to samples, it still needs to
> reject invalid callchains across the losts.  Maybe it can just flush
> pending samples when it sees LOST records and not try to match them but
> having the cookies will handle it more accurately as some callchains may
> be valid after the LOST.

Sure, I can add that back, with the added comments needed that Jens
suggested.

Thanks,

-- Steve