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Subject: Re: [RFC PATCH 0/6] [RFC] Faultable tracepoints (v2)
To:     Steven Rostedt <rostedt@goodmis.org>
Cc:     linux-kernel@vger.kernel.org,
        Peter Zijlstra <peterz@infradead.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Yonghong Song <yhs@fb.com>,
        "Paul E . McKenney" <paulmck@kernel.org>,
        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>,
        Joel Fernandes <joel@joelfernandes.org>, bpf@vger.kernel.org,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
References: <20210218222125.46565-1-mjeanson@efficios.com>
 <20210223211639.670db85c@gandalf.local.home>
From:   Michael Jeanson <mjeanson@efficios.com>
Message-ID: <083bce0f-bd66-ab83-1211-be9838499b45@efficios.com>
Date:   Wed, 24 Feb 2021 11:22:03 -0500
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[ Adding Mathieu Desnoyers in CC ]

On 2021-02-23 21 h 16, Steven Rostedt wrote:
> On Thu, 18 Feb 2021 17:21:19 -0500
> Michael Jeanson <mjeanson@efficios.com> wrote:
> 
>> This series only implements the tracepoint infrastructure required to
>> allow tracers to handle page faults. Modifying each tracer to handle
>> those page faults would be a next step after we all agree on this piece
>> of instrumentation infrastructure.
> 
> I started taking a quick look at this, and came up with the question: how
> do you allow preemption when dealing with per-cpu buffers or storage to
> record the data?
> 
> That is, perf, bpf and ftrace are all using some kind of per-cpu data, and
> this is the reason for the need to disable preemption. What's the solution
> that LTTng is using for this? I know it has a per cpu buffers too, but does
> it have some kind of "per task" buffer that is being used to extract the
> data that can fault?
> 
> -- Steve
>