From: Steven Rostedt <rostedt@goodmis.org>
To: linux-kernel@vger.kernel.org
Cc: Ingo Molnar <mingo@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Subject: [for-next][PATCH 09/12] tracing: Show the preempt count of when the event was called
Date: Sun, 03 Jul 2016 16:33:11 -0400 [thread overview]
Message-ID: <20160703203335.426689631@goodmis.org> (raw)
In-Reply-To: 20160703203302.877954992@goodmis.org
[-- Attachment #1: 0009-tracing-Show-the-preempt-count-of-when-the-event-was.patch --]
[-- Type: text/plain, Size: 1504 bytes --]
From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>
Because tracepoint callbacks are done with preemption enabled, the trace
events are always called with preempt disable due to the
rcu_read_lock_sched_notrace() in __DO_TRACE(). This causes the preempt count
shown in the recorded trace event to be inaccurate. It is always one more
that what the preempt_count was when the tracepoint was called.
If CONFIG_PREEMPT is enabled, subtract 1 from the preempt_count before
recording it in the trace buffer.
Link: http://lkml.kernel.org/r/20160525132537.GA10808@linutronix.de
Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
kernel/trace/trace_events.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index fd449eb138cf..03c0a48c3ac4 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -261,6 +261,14 @@ void *trace_event_buffer_reserve(struct trace_event_buffer *fbuffer,
local_save_flags(fbuffer->flags);
fbuffer->pc = preempt_count();
+ /*
+ * If CONFIG_PREEMPT is enabled, then the tracepoint itself disables
+ * preemption (adding one to the preempt_count). Since we are
+ * interested in the preempt_count at the time the tracepoint was
+ * hit, we need to subtract one to offset the increment.
+ */
+ if (IS_ENABLED(CONFIG_PREEMPT))
+ fbuffer->pc--;
fbuffer->trace_file = trace_file;
fbuffer->event =
--
2.8.1
next prev parent reply other threads:[~2016-07-03 20:34 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-03 20:33 [for-next][PATCH 00/12] tracing: Updates for 4.8 Steven Rostedt
2016-07-03 20:33 ` [for-next][PATCH 01/12] tracing: Make the pid filtering helper functions global Steven Rostedt
2016-07-03 20:33 ` [for-next][PATCH 02/12] tracing: Move filtered_pid helper functions into trace.c Steven Rostedt
2016-07-03 20:33 ` [for-next][PATCH 03/12] tracing: Move the pid_list seq_file functions to be global Steven Rostedt
2016-07-03 20:33 ` [for-next][PATCH 04/12] tracing: Move pid_list write processing into its own function Steven Rostedt
2016-07-03 20:33 ` [for-next][PATCH 05/12] ftrace: Have set_ftrace_pid use the bitmap like events do Steven Rostedt
2016-07-03 20:33 ` [for-next][PATCH 06/12] tracing: expose current->comm to [ku]probe events Steven Rostedt
2016-07-03 20:33 ` [for-next][PATCH 07/12] tracing: Choose static tp_printk buffer by explicit nesting count Steven Rostedt
2016-07-03 20:33 ` [for-next][PATCH 08/12] tracing: Add trace_printk sample code Steven Rostedt
2016-07-03 20:33 ` Steven Rostedt [this message]
2016-07-03 20:33 ` [for-next][PATCH 10/12] tracing: Expose CPU physical addresses (resource values) for PCI devices Steven Rostedt
2016-07-03 20:33 ` [for-next][PATCH 11/12] tracing: Skip more functions when doing stack tracing of events Steven Rostedt
2016-07-03 20:33 ` [for-next][PATCH 12/12] tracing/function_graph: Fix filters for function_graph threshold Steven Rostedt
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20160703203335.426689631@goodmis.org \
--to=rostedt@goodmis.org \
--cc=akpm@linux-foundation.org \
--cc=bigeasy@linutronix.de \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).