linux-kernel - [PATCH 13/22] tracing: Reset ring buffer when changing trace

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Message-Id: <20121102133500.337156347@goodmis.org>
Date:	Fri, 02 Nov 2012 09:33:05 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	linux-kernel@...r.kernel.org
Cc:	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	David Sharp <dhsharp@...gle.com>
Subject: [PATCH 13/22] tracing: Reset ring buffer when changing trace_clocks

From: David Sharp <dhsharp@...gle.com>

Because the "tsc" clock isn't in nanoseconds, the ring buffer must be
reset when changing clocks so that incomparable timestamps don't end up
in the same trace.

Tested: Confirmed switching clocks resets the trace buffer.

Google-Bug-Id: 6980623
Link: http://lkml.kernel.org/r/1349998076-15495-3-git-send-email-dhsharp@google.com

Cc: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Signed-off-by: David Sharp <dhsharp@...gle.com>
Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
---
 kernel/trace/trace.c |    8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index d7d6c52..d598ede 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4074,6 +4074,14 @@ static ssize_t tracing_clock_write(struct file *filp, const char __user *ubuf,
 	if (max_tr.buffer)
 		ring_buffer_set_clock(max_tr.buffer, trace_clocks[i].func);
 
+	/*
+	 * New clock may not be consistent with the previous clock.
+	 * Reset the buffer so that it doesn't have incomparable timestamps.
+	 */
+	tracing_reset_online_cpus(&global_trace);
+	if (max_tr.buffer)
+		tracing_reset_online_cpus(&max_tr);
+
 	mutex_unlock(&trace_types_lock);
 
 	*fpos += cnt;
-- 
1.7.10.4



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