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Message-ID: <20240913130834.hq4gj27fcklakkzb@treble>
Date: Fri, 13 Sep 2024 06:08:34 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Namhyung Kim <namhyung@...nel.org>,
Steven Rostedt <rostedt@...dmis.org>,
Ingo Molnar <mingo@...nel.org>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
linux-kernel@...r.kernel.org, x86@...nel.org,
Indu Bhagat <indu.bhagat@...cle.com>,
Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
Adrian Hunter <adrian.hunter@...el.com>,
linux-perf-users@...r.kernel.org, Mark Brown <broonie@...nel.org>,
linux-toolchains@...r.kernel.org
Subject: Re: [PATCH RFC 04/10] perf: Introduce deferred user callchains
On Mon, Nov 20, 2023 at 03:03:34PM +0100, Peter Zijlstra wrote:
> On Wed, Nov 15, 2023 at 08:13:31AM -0800, Namhyung Kim wrote:
>
> > ---8<---
> > diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> > index 39c6a250dd1b..a3765ff59798 100644
> > --- a/include/uapi/linux/perf_event.h
> > +++ b/include/uapi/linux/perf_event.h
> > @@ -456,7 +456,8 @@ struct perf_event_attr {
> > inherit_thread : 1, /* children only inherit if cloned with CLONE_THREAD */
> > remove_on_exec : 1, /* event is removed from task on exec */
> > sigtrap : 1, /* send synchronous SIGTRAP on event */
> > - __reserved_1 : 26;
> > + defer_callchain: 1, /* generate DEFERRED_CALLCHAINS records for userspace */
> > + __reserved_1 : 25;
> >
> > union {
> > __u32 wakeup_events; /* wakeup every n events */
> > @@ -1207,6 +1208,20 @@ enum perf_event_type {
> > */
> > PERF_RECORD_AUX_OUTPUT_HW_ID = 21,
> >
> > + /*
> > + * Deferred user stack callchains (for SFrame). Previous samples would
>
> Possibly also useful for ShadowStack based unwinders. And by virtue of
> it possibly saving work when multiple consecutive samples hit
> the same kernel section, for everything.
[ necroing old thread as I'm finally working on a v2 ]
Peter, can you elaborate? What did you mean by "same kernel section"?
Like if there's a duplicate kernel callchain? Or something else?
--
Josh
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