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From: Hiraku Toyooka <hiraku.toyooka.gu@hitachi.com>
To: rostedt@goodmis.org
Cc: masami.hiramatsu.pt@hitachi.com,
	Frederic Weisbecker <fweisbec@gmail.com>,
	Ingo Molnar <mingo@redhat.com>,
	linux-kernel@vger.kernel.org, yrl.pp-manager.tt@hitachi.com
Subject: [PATCH v4 -tip 1/3] tracing: replace static old_tracer with trace iterator's pointer to the original tracer's name
Date: Wed, 26 Dec 2012 11:52:52 +0900	[thread overview]
Message-ID: <20121226025252.3252.9276.stgit@liselsia> (raw)
In-Reply-To: <20121226025243.3252.61095.stgit@liselsia>

Currently the trace buffer read functions use a static variable
"old_tracer" for detecting if the current tracer changes. This
was suitable for a single trace file ("trace"), but to add a
snapshot feature that will use the same function for its file,
a check against a static variable is not sufficient.

To use the output functions for two different files, instead of
storing the current tracer in a static variable, as the trace
iterator descriptor contains a pointer to the original current
tracer's name, that pointer can now be used to check if the
current tracer has changed between different reads of the trace
file.

Signed-off-by: Hiraku Toyooka <hiraku.toyooka.gu@hitachi.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: linux-kernel@vger.kernel.org
---
 kernel/trace/trace.c |   22 +++++++++-------------
 1 file changed, 9 insertions(+), 13 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index a8ce008..1787304 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1948,18 +1948,20 @@ void tracing_iter_reset(struct trace_iterator *iter, int cpu)
 static void *s_start(struct seq_file *m, loff_t *pos)
 {
 	struct trace_iterator *iter = m->private;
-	static struct tracer *old_tracer;
 	int cpu_file = iter->cpu_file;
 	void *p = NULL;
 	loff_t l = 0;
 	int cpu;
 
-	/* copy the tracer to avoid using a global lock all around */
+	/*
+	 * copy the tracer to avoid using a global lock all around.
+	 * iter->trace is a copy of current_trace, the pointer to the
+	 * name may be used instead of a strcmp(), as iter->trace->name
+	 * will point to the same string as current_trace->name.
+	 */
 	mutex_lock(&trace_types_lock);
-	if (unlikely(old_tracer != current_trace && current_trace)) {
-		old_tracer = current_trace;
+	if (unlikely(current_trace && iter->trace->name != current_trace->name))
 		*iter->trace = *current_trace;
-	}
 	mutex_unlock(&trace_types_lock);
 
 	atomic_inc(&trace_record_cmdline_disabled);
@@ -3481,7 +3483,6 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
 		  size_t cnt, loff_t *ppos)
 {
 	struct trace_iterator *iter = filp->private_data;
-	static struct tracer *old_tracer;
 	ssize_t sret;
 
 	/* return any leftover data */
@@ -3493,10 +3494,8 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
 
 	/* copy the tracer to avoid using a global lock all around */
 	mutex_lock(&trace_types_lock);
-	if (unlikely(old_tracer != current_trace && current_trace)) {
-		old_tracer = current_trace;
+	if (unlikely(current_trace && iter->trace->name != current_trace->name))
 		*iter->trace = *current_trace;
-	}
 	mutex_unlock(&trace_types_lock);
 
 	/*
@@ -3652,7 +3651,6 @@ static ssize_t tracing_splice_read_pipe(struct file *filp,
 		.ops		= &tracing_pipe_buf_ops,
 		.spd_release	= tracing_spd_release_pipe,
 	};
-	static struct tracer *old_tracer;
 	ssize_t ret;
 	size_t rem;
 	unsigned int i;
@@ -3662,10 +3660,8 @@ static ssize_t tracing_splice_read_pipe(struct file *filp,
 
 	/* copy the tracer to avoid using a global lock all around */
 	mutex_lock(&trace_types_lock);
-	if (unlikely(old_tracer != current_trace && current_trace)) {
-		old_tracer = current_trace;
+	if (unlikely(current_trace && iter->trace->name != current_trace->name))
 		*iter->trace = *current_trace;
-	}
 	mutex_unlock(&trace_types_lock);
 
 	mutex_lock(&iter->mutex);


  reply	other threads:[~2012-12-26  2:53 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-12-26  2:52 [PATCH v4 -tip 0/3] tracing: make a snapshot feature available from userspace Hiraku Toyooka
2012-12-26  2:52 ` Hiraku Toyooka [this message]
2013-02-03 19:23   ` [tip:perf/core] tracing: Replace static old_tracer check of tracer name tip-bot for Hiraku Toyooka
2012-12-26  2:53 ` [PATCH v4 -tip 2/3] tracing: make a snapshot feature available from userspace Hiraku Toyooka
2013-02-03 19:25   ` [tip:perf/core] tracing: Make " tip-bot for Hiraku Toyooka
2012-12-26  2:53 ` [PATCH v4 -tip 3/3] tracing: add description of snapshot to Documentation/trace/ftrace.txt Hiraku Toyooka
2013-02-03 19:26   ` [tip:perf/core] tracing: Add documentation of snapshot utility tip-bot for Hiraku Toyooka

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