Message-ID: <20250916104109.23319785@gandalf.local.home>
Date: Tue, 16 Sep 2025 10:41:09 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: 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>, Ingo Molnar <mingo@...nel.org>, Jiri
 Olsa <jolsa@...nel.org>, Arnaldo Carvalho de Melo <acme@...nel.org>,
 Namhyung Kim <namhyung@...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>, Florian Weimer <fweimer@...hat.com>, Sam James
 <sam@...too.org>, Kees Cook <kees@...nel.org>, "Carlos O'Donell"
 <codonell@...hat.com>
Subject: Re: [RESEND][PATCH v15 0/4] perf: Support the deferred unwinding
 infrastructure

Peter,

It's been over 3 weeks since the original has been sent. And last week I
broke it up to only hold the kernel changes. Can you please take a look at
it?

I have updated the user space side with Namhyung Kim's updates:

   https://lore.kernel.org/all/20250908175319.841517121@kernel.org/

Also, the two patches to enable deferred unwinding in x86 has been ignored
for almost three weeks as well:

  https://lore.kernel.org/linux-trace-kernel/20250827193644.527334838@kernel.org/

-- Steve


On Mon, 8 Sep 2025 13:21:06 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> Peter, can you take a look at these patches please. I believe you're the
> only one that really maintains this code today.
> 
> -- Steve
> 
> 
> On Mon, 08 Sep 2025 13:14:12 -0400
> Steven Rostedt <rostedt@...nel.org> wrote:
> 
> > [
> >   This is simply a resend of version 15 of this patch series
> >   but with only the kernel changes. I'm separating out the user space
> >   changes to their own series.
> >   The original v15 is here:
> >     https://lore.kernel.org/linux-trace-kernel/20250825180638.877627656@kernel.org/
> > ]
> > 
> > This patch set is based off of perf/core of the tip tree:
> >   git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git
> > 
> > To run this series, you can checkout this repo that has this series as well as the above:
> > 
> >   git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace.git  unwind/perf-test
> > 
> > This series implements the perf interface to use deferred user space stack
> > tracing.
> > 
> > Patch 1 adds a new API interface to the user unwinder logic to allow perf to
> > get the current context cookie for it's task event tracing. Perf's task event
> > tracing maps a single task per perf event buffer and it follows the task
> > around, so it only needs to implement its own task_work to do the deferred
> > stack trace. Because it can still suffer not knowing which user stack trace
> > belongs to which kernel stack due to dropped events, having the cookie to
> > create a unique identifier for each user space stack trace to know which
> > kernel stack to append it to is useful.
> > 
> > Patch 2 adds the per task deferred stack traces to perf. It adds a new event
> > type called PERF_RECORD_CALLCHAIN_DEFERRED that is recorded when a task is
> > about to go back to user space and happens in a location that pages may be
> > faulted in. It also adds a new callchain context called PERF_CONTEXT_USER_DEFERRED
> > that is used as a place holder in a kernel callchain to append the deferred
> > user space stack trace to.
> > 
> > Patch 3 adds the user stack trace context cookie in the kernel callchain right
> > after the PERF_CONTEXT_USER_DEFERRED context so that the user space side can
> > map the request to the deferred user space stack trace.
> > 
> > Patch 4 adds support for the per CPU perf events that will allow the kernel to
> > associate each of the per CPU perf event buffers to a single application. This
> > is needed so that when a request for a deferred stack trace happens on a task
> > that then migrates to another CPU, it will know which CPU buffer to use to
> > record the stack trace on. It is possible to have more than one perf user tool
> > running and a request made by one perf tool should have the deferred trace go
> > to the same perf tool's perf CPU event buffer. A global list of all the
> > descriptors representing each perf tool that is using deferred stack tracing
> > is created to manage this.
> > 
> > 
> > Josh Poimboeuf (1):
> >       perf: Support deferred user callchains
> > 
> > Steven Rostedt (3):
> >       unwind deferred: Add unwind_user_get_cookie() API
> >       perf: Have the deferred request record the user context cookie
> >       perf: Support deferred user callchains for per CPU events
> > 
> > ----
> >  include/linux/perf_event.h            |  11 +-
> >  include/linux/unwind_deferred.h       |   5 +
> >  include/uapi/linux/perf_event.h       |  25 +-
> >  kernel/bpf/stackmap.c                 |   4 +-
> >  kernel/events/callchain.c             |  14 +-
> >  kernel/events/core.c                  | 421 +++++++++++++++++++++++++++++++++-
> >  kernel/unwind/deferred.c              |  21 ++
> >  tools/include/uapi/linux/perf_event.h |  25 +-
> >  8 files changed, 518 insertions(+), 8 deletions(-)  
> 

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