From: Daniel Bristot de Oliveira <bristot@redhat.com>
To: linux-kernel@vger.kernel.org
Cc: Steven Rostedt <rostedt@goodmis.org>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Ingo Molnar <mingo@redhat.com>, Andy Lutomirski <luto@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Borislav Petkov <bp@alien8.de>,
Peter Zijlstra <peterz@infradead.org>,
"H. Peter Anvin" <hpa@zytor.com>,
"Joel Fernandes (Google)" <joel@joelfernandes.org>,
Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Tommaso Cucinotta <tommaso.cucinotta@santannapisa.it>,
Romulo Silva de Oliveira <romulo.deoliveira@ufsc.br>,
Clark Williams <williams@redhat.com>,
x86@kernel.org
Subject: [RFC PATCH 0/7] Early task context tracking
Date: Tue, 2 Apr 2019 22:03:52 +0200 [thread overview]
Message-ID: <cover.1554234787.git.bristot@redhat.com> (raw)
Note: do not take it too seriously, it is just a proof of concept.
Some time ago, while using perf to check the automaton model, I noticed
that perf was losing events. The same was reproducible with ftrace.
See: https://www.spinics.net/lists/linux-rt-users/msg19781.html
Steve pointed to a problem in the identification of the context
execution used by the recursion control.
Currently, recursion control uses the preempt_counter to
identify the current context. The NMI/HARD/SOFT IRQ counters
are set in the preempt_counter in the irq_enter/exit functions.
In a trace, they are set like this:
-------------- %< --------------------
0) ==========> |
0) | do_IRQ() { /* First C function */
0) | irq_enter() {
0) | /* set the IRQ context. */
0) 1.081 us | }
0) | handle_irq() {
0) | /* IRQ handling code */
0) + 10.290 us | }
0) | irq_exit() {
0) | /* unset the IRQ context. */
0) 6.657 us | }
0) + 18.995 us | }
0) <========== |
-------------- >% --------------------
As one can see, functions (and events) that take place before the set
and after unset the preempt_counter are identified in the wrong context,
causing the miss interpretation that a recursion is taking place.
When this happens, events are dropped.
To resolve this problem, the set/unset of the IRQ/NMI context needs to
be done before the execution of the first C execution, and after its
return. By doing so, and using this method to identify the context in the
trace recursion protection, no more events are lost.
A possible solution is to use a per-cpu variable set and unset in the
entry point of NMI/IRQs, before calling the C handler. This possible
solution is presented in the next patches as a proof of concept, for
x86_64. However, other ideas might be better than mine... so...
Daniel Bristot de Oliveira (7):
x86/entry: Add support for early task context tracking
trace: Move the trace recursion context enum to trace.h and reuse it
trace: Optimize trace_get_context_bit()
trace/ring_buffer: Use trace_get_context_bit()
trace: Use early task context tracking if available
events: Create an trace_get_context_bit()
events: Use early task context tracking if available
arch/x86/entry/entry_64.S | 9 ++++++
arch/x86/include/asm/irqflags.h | 30 ++++++++++++++++++++
arch/x86/kernel/cpu/common.c | 4 +++
include/linux/irqflags.h | 4 +++
kernel/events/internal.h | 50 +++++++++++++++++++++++++++------
kernel/softirq.c | 5 +++-
kernel/trace/ring_buffer.c | 28 ++----------------
kernel/trace/trace.h | 46 ++++++++++++++++++++++--------
8 files changed, 129 insertions(+), 47 deletions(-)
--
2.20.1
next reply other threads:[~2019-04-02 20:04 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-02 20:03 Daniel Bristot de Oliveira [this message]
2019-04-02 20:03 ` [RFC PATCH 1/7] x86/entry: Add support for early task context tracking Daniel Bristot de Oliveira
2019-04-02 20:03 ` [RFC PATCH 2/7] trace: Move the trace recursion context enum to trace.h and reuse it Daniel Bristot de Oliveira
2019-04-02 20:03 ` [RFC PATCH 3/7] trace: Optimize trace_get_context_bit() Daniel Bristot de Oliveira
2019-04-02 20:03 ` [RFC PATCH 4/7] trace/ring_buffer: Use trace_get_context_bit() Daniel Bristot de Oliveira
2019-04-02 20:03 ` [RFC PATCH 5/7] trace: Use early task context tracking if available Daniel Bristot de Oliveira
2019-04-02 20:03 ` [RFC PATCH 6/7] events: Create an trace_get_context_bit() Daniel Bristot de Oliveira
2019-04-02 20:03 ` [RFC PATCH 7/7] events: Use early task context tracking if available Daniel Bristot de Oliveira
2019-04-04 0:01 ` [RFC PATCH 0/7] Early task context tracking Andy Lutomirski
2019-04-04 9:42 ` Peter Zijlstra
2019-04-08 12:47 ` Daniel Bristot de Oliveira
2019-04-08 16:08 ` Andy Lutomirski
2019-04-04 17:40 ` Joel Fernandes
2019-04-08 12:54 ` Daniel Bristot de Oliveira
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