linux-kernel - Re: [PATCH v3 11/19] unwind: Add deferred user space unwinding API

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Message-ID: <20241029165134.zoeh5vg6b4lmac2d@treble.attlocal.net>
Date: Tue, 29 Oct 2024 09:51:34 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: x86@...nel.org, Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	linux-kernel@...r.kernel.org, Indu Bhagat <indu.bhagat@...cle.com>,
	Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>, Namhyung Kim <namhyung@...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, Jordan Rome <jordalgo@...a.com>,
	Sam James <sam@...too.org>, linux-trace-kernel@...r.kerne.org,
	Andrii Nakryiko <andrii.nakryiko@...il.com>,
	Jens Remus <jremus@...ux.ibm.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Florian Weimer <fweimer@...hat.com>,
	Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH v3 11/19] unwind: Add deferred user space unwinding API

On Tue, Oct 29, 2024 at 02:48:07PM +0100, Peter Zijlstra wrote:
> On Mon, Oct 28, 2024 at 02:47:38PM -0700, Josh Poimboeuf wrote:
> 
> > +/*
> > + * The "context cookie" is a unique identifier which allows post-processing to
> > + * correlate kernel trace(s) with user unwinds.  It has the CPU id the highest
> > + * 16 bits and a per-CPU entry counter in the lower 48 bits.
> > + */
> > +static u64 ctx_to_cookie(u64 cpu, u64 ctx)
> > +{
> > +	BUILD_BUG_ON(NR_CPUS > 65535);
> > +	return (ctx & ((1UL << 48) - 1)) | cpu;
> > +}
> 
> Did you mean to: (cpu << 48) ?

Indeed... that was the victim of a late refactoring.

-- 
Josh