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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        "Srivatsa S. Bhat (VMware)" <srivatsa@csail.mit.edu>,
        "Steven Rostedt (VMware)" <rostedt@goodmis.org>
Subject: [PATCH 4.9 89/92] tracing/hwlat: Dont ignore outer-loop duration when calculating max_latency
Date:   Wed, 16 Oct 2019 14:51:02 -0700
Message-Id: <20191016214848.563153457@linuxfoundation.org>
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From: Srivatsa S. Bhat (VMware) <srivatsa@csail.mit.edu>

commit fc64e4ad80d4b72efce116f87b3174f0b7196f8e upstream.

max_latency is intended to record the maximum ever observed hardware
latency, which may occur in either part of the loop (inner/outer). So
we need to also consider the outer-loop sample when updating
max_latency.

Link: http://lkml.kernel.org/r/157073345463.17189.18124025522664682811.stgit@srivatsa-ubuntu

Fixes: e7c15cd8a113 ("tracing: Added hardware latency tracer")
Cc: stable@vger.kernel.org
Signed-off-by: Srivatsa S. Bhat (VMware) <srivatsa@csail.mit.edu>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 kernel/trace/trace_hwlat.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/kernel/trace/trace_hwlat.c
+++ b/kernel/trace/trace_hwlat.c
@@ -257,6 +257,8 @@ static int get_sample(void)
 		/* Keep a running maximum ever recorded hardware latency */
 		if (sample > tr->max_latency)
 			tr->max_latency = sample;
+		if (outer_sample > tr->max_latency)
+			tr->max_latency = outer_sample;
 	}
 
 out: