linux-kernel - Re: [PATCH v5 13/17] perf: Support deferred user callchains

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Message-ID: <20250508145439.4c6482b7@gandalf.local.home>
Date: Thu, 8 May 2025 14:54:39 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
 Namhyung Kim <namhyung@...nel.org>, Masami Hiramatsu <mhiramat@...nel.org>,
 Mark Rutland <mark.rutland@....com>, Andrew Morton
 <akpm@...ux-foundation.org>, Josh Poimboeuf <jpoimboe@...nel.org>,
 x86@...nel.org, Peter Zijlstra <peterz@...radead.org>, Ingo Molnar
 <mingo@...nel.org>, Arnaldo Carvalho de Melo <acme@...nel.org>, Indu Bhagat
 <indu.bhagat@...cle.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, Jordan Rome <jordalgo@...a.com>, Sam
 James <sam@...too.org>, Andrii Nakryiko <andrii.nakryiko@...il.com>, Jens
 Remus <jremus@...ux.ibm.com>, Florian Weimer <fweimer@...hat.com>, Andy
 Lutomirski <luto@...nel.org>, Weinan Liu <wnliu@...gle.com>, Blake Jones
 <blakejones@...gle.com>, Beau Belgrave <beaub@...ux.microsoft.com>, "Jose
 E. Marchesi" <jemarch@....org>
Subject: Re: [PATCH v5 13/17] perf: Support deferred user callchains

On Thu, 8 May 2025 14:49:59 -0400
Mathieu Desnoyers <mathieu.desnoyers@...icios.com> wrote:

> AFAIR, the cookie method generates the cookie by combining the cpu
> number with a per-cpu count.
> 
> This ensures that there are not two cookies emitted at the same time
> from two CPUs that have the same value by accident.
> 
> How would the timestamp method prevent this ?

Do we care? It only needs to be unique per pid doesn't it?

-- Steve