From: Peter Zijlstra <peterz@infradead.org>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: "Paul E. McKenney" <paulmck@kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
Masami Hiramatsu <mhiramat@kernel.org>,
linux-kernel@vger.kernel.org,
Michael Jeanson <mjeanson@efficios.com>,
Alexei Starovoitov <ast@kernel.org>, Yonghong Song <yhs@fb.com>,
Ingo Molnar <mingo@redhat.com>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
bpf@vger.kernel.org, Joel Fernandes <joel@joelfernandes.org>
Subject: Re: [PATCH v4 1/5] tracing: Introduce faultable tracepoints
Date: Tue, 21 Nov 2023 15:36:47 +0100 [thread overview]
Message-ID: <20231121143647.GI8262@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <a0ac5f77-411e-4562-9863-81196238f3f5@efficios.com>
On Tue, Nov 21, 2023 at 09:06:18AM -0500, Mathieu Desnoyers wrote:
> Task trace RCU fits a niche that has the following set of requirements/tradeoffs:
>
> - Allow page faults within RCU read-side (like SRCU),
> - Has a low-overhead read lock-unlock (without the memory barrier overhead of SRCU),
> - The tradeoff: Has a rather slow synchronize_rcu(), but tracers should not care about
> that. Hence, this is not meant to be a generic replacement for SRCU.
>
> Based on my reading of https://lwn.net/Articles/253651/ , preemptible RCU is not a good
> fit for the following reasons:
>
> - It disallows blocking within a RCU read-side on non-CONFIG_PREEMPT kernels,
Your counter points are confused, we simply don't build preemptible RCU
unless PREEMPT=y, but that could surely be fixed and exposed as a
separate flavour.
> - AFAIU the mmap_sem used within the page fault handler does not have priority inheritance.
What's that got to do with anything?
Still utterly confused about what task-tracing rcu is and how it is
different from preemptible rcu.
next prev parent reply other threads:[~2023-11-21 14:37 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-11-20 20:54 [PATCH v4 0/5] Faultable Tracepoints Mathieu Desnoyers
2023-11-20 20:54 ` [PATCH v4 1/5] tracing: Introduce faultable tracepoints Mathieu Desnoyers
2023-11-20 21:47 ` Peter Zijlstra
2023-11-20 22:18 ` Paul E. McKenney
2023-11-20 22:23 ` Peter Zijlstra
2023-11-20 23:56 ` Paul E. McKenney
2023-11-21 8:47 ` Peter Zijlstra
2023-11-21 14:06 ` Mathieu Desnoyers
2023-11-21 14:36 ` Peter Zijlstra [this message]
2023-11-21 14:40 ` Mathieu Desnoyers
2023-11-21 14:46 ` Peter Zijlstra
2023-11-21 14:56 ` Mathieu Desnoyers
2023-11-21 15:51 ` Paul E. McKenney
2023-11-21 15:52 ` Peter Zijlstra
2023-11-21 16:00 ` Mathieu Desnoyers
2023-11-21 16:07 ` Steven Rostedt
2023-11-21 16:11 ` Mathieu Desnoyers
2023-11-21 16:43 ` Paul E. McKenney
2023-11-21 16:50 ` Peter Zijlstra
2023-11-21 17:31 ` Peter Zijlstra
2023-11-21 16:41 ` Paul E. McKenney
2023-11-21 14:44 ` Steven Rostedt
2023-11-21 16:45 ` Paul E. McKenney
2023-11-21 15:58 ` Paul E. McKenney
2023-11-21 16:03 ` Peter Zijlstra
2023-11-21 16:46 ` Paul E. McKenney
2023-11-20 22:20 ` Steven Rostedt
2024-06-20 15:38 ` Mathieu Desnoyers
2023-11-20 20:54 ` [PATCH v4 2/5] tracing/ftrace: Add support for " Mathieu Desnoyers
2023-11-20 22:15 ` Peter Zijlstra
2024-06-20 15:04 ` Mathieu Desnoyers
2023-11-20 20:54 ` [PATCH v4 3/5] tracing/bpf-trace: add " Mathieu Desnoyers
2023-11-20 20:54 ` [PATCH v4 4/5] tracing/perf: " Mathieu Desnoyers
2023-11-20 20:54 ` [PATCH v4 5/5] tracing: convert sys_enter/exit to " Mathieu Desnoyers
2023-11-20 21:46 ` Peter Zijlstra
2024-06-20 15:05 ` Mathieu Desnoyers
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