From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org,
Namhyung Kim <namhyung@kernel.org>,
Masami Hiramatsu <mhiramat@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Andrew Morton <akpm@linux-foundation.org>,
Josh Poimboeuf <jpoimboe@kernel.org>,
x86@kernel.org, Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Indu Bhagat <indu.bhagat@oracle.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Jiri Olsa <jolsa@kernel.org>, Ian Rogers <irogers@google.com>,
Adrian Hunter <adrian.hunter@intel.com>,
linux-perf-users@vger.kernel.org, Mark Brown <broonie@kernel.org>,
linux-toolchains@vger.kernel.org, Jordan Rome <jordalgo@meta.com>,
Sam James <sam@gentoo.org>,
Andrii Nakryiko <andrii.nakryiko@gmail.com>,
Jens Remus <jremus@linux.ibm.com>,
Florian Weimer <fweimer@redhat.com>,
Andy Lutomirski <luto@kernel.org>, Weinan Liu <wnliu@google.com>,
Blake Jones <blakejones@google.com>,
Beau Belgrave <beaub@linux.microsoft.com>,
"Jose E. Marchesi" <jemarch@gnu.org>
Subject: Re: [PATCH v5 13/17] perf: Support deferred user callchains
Date: Fri, 9 May 2025 08:23:49 -0400 [thread overview]
Message-ID: <8889c16b-9c3d-4ab3-b353-e00146532174@efficios.com> (raw)
In-Reply-To: <20250508145439.4c6482b7@gandalf.local.home>
On 2025-05-08 14:54, Steven Rostedt wrote:
> On Thu, 8 May 2025 14:49:59 -0400
> Mathieu Desnoyers <mathieu.desnoyers@efficios.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?
Is it possible to have many threads writing into the same
ring buffer in that scenario ? Are all event records stamped
with their associated PID ? As long as we have enough information
to know which thread was associated with the timestamp cookie
on both ends (request for callchain and saving the user callchain
on return to userspace), we should be OK.
Thanks,
Mathieu
--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com
next prev parent reply other threads:[~2025-05-09 12:23 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-04-24 16:25 [PATCH v5 00/17] perf: Deferred unwinding of user space stack traces Steven Rostedt
2025-04-24 16:25 ` [PATCH v5 01/17] unwind_user: Add user space unwinding API Steven Rostedt
2025-04-24 16:25 ` [PATCH v5 02/17] unwind_user: Add frame pointer support Steven Rostedt
2025-04-24 16:25 ` [PATCH v5 03/17] unwind_user/x86: Enable frame pointer unwinding on x86 Steven Rostedt
2025-04-24 16:25 ` [PATCH v5 04/17] perf/x86: Rename and move get_segment_base() and make it global Steven Rostedt
2025-04-24 16:25 ` [PATCH v5 05/17] unwind_user: Add compat mode frame pointer support Steven Rostedt
2025-04-24 16:25 ` [PATCH v5 06/17] unwind_user/x86: Enable compat mode frame pointer unwinding on x86 Steven Rostedt
2025-04-24 16:25 ` [PATCH v5 07/17] unwind_user/deferred: Add unwind_deferred_trace() Steven Rostedt
2025-04-24 16:25 ` [PATCH v5 08/17] unwind_user/deferred: Add unwind cache Steven Rostedt
2025-04-24 19:00 ` Steven Rostedt
2025-04-24 16:25 ` [PATCH v5 09/17] perf: Remove get_perf_callchain() init_nr argument Steven Rostedt
2025-04-24 16:25 ` [PATCH v5 10/17] perf: Have get_perf_callchain() return NULL if crosstask and user are set Steven Rostedt
2025-04-24 16:25 ` [PATCH v5 11/17] perf: Simplify get_perf_callchain() user logic Steven Rostedt
2025-04-24 16:36 ` Peter Zijlstra
2025-04-24 17:28 ` Steven Rostedt
2025-04-24 17:42 ` Mathieu Desnoyers
2025-04-24 17:47 ` Steven Rostedt
2025-04-25 7:13 ` Peter Zijlstra
2025-04-24 16:25 ` [PATCH v5 12/17] perf: Skip user unwind if !current->mm Steven Rostedt
2025-04-24 16:37 ` Peter Zijlstra
2025-04-24 17:01 ` Steven Rostedt
2025-04-24 16:25 ` [PATCH v5 13/17] perf: Support deferred user callchains Steven Rostedt
2025-04-24 16:38 ` Peter Zijlstra
2025-04-24 17:16 ` Steven Rostedt
2025-04-25 15:24 ` Namhyung Kim
2025-04-25 16:58 ` Steven Rostedt
2025-04-28 20:42 ` Namhyung Kim
2025-04-28 22:02 ` Steven Rostedt
2025-04-29 0:29 ` Namhyung Kim
2025-04-29 14:00 ` Steven Rostedt
2025-05-08 16:03 ` Steven Rostedt
2025-05-08 18:44 ` Namhyung Kim
2025-05-08 18:49 ` Mathieu Desnoyers
2025-05-08 18:54 ` Steven Rostedt
2025-05-09 12:23 ` Mathieu Desnoyers [this message]
2025-05-09 15:45 ` Namhyung Kim
2025-05-09 15:55 ` Steven Rostedt
2025-04-24 16:25 ` [PATCH v5 14/17] perf tools: Minimal CALLCHAIN_DEFERRED support Steven Rostedt
2025-04-24 16:25 ` [PATCH v5 15/17] perf record: Enable defer_callchain for user callchains Steven Rostedt
2025-04-24 16:25 ` [PATCH v5 16/17] perf script: Display PERF_RECORD_CALLCHAIN_DEFERRED Steven Rostedt
2025-04-24 16:25 ` [PATCH v5 17/17] perf tools: Merge deferred user callchains Steven Rostedt
2025-04-24 17:04 ` [PATCH v5 00/17] perf: Deferred unwinding of user space stack traces Steven Rostedt
2025-04-24 18:32 ` Miguel Ojeda
2025-04-24 18:41 ` Steven Rostedt
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