linux-kernel - [PATCH 2/3] tracing/hwlat: Don't ignore outer-loop duration when calculating max

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Date:   Thu, 10 Oct 2019 11:51:01 -0700
From:   "Srivatsa S. Bhat" <srivatsa@...il.mit.edu>
To:     linux-kernel@...r.kernel.org, rostedt@...dmis.org, mingo@...hat.com
Cc:     amakhalov@...are.com, akaher@...are.com, anishs@...are.com,
        bordoloih@...are.com, srivatsab@...are.com, srivatsa@...il.mit.edu
Subject: [PATCH 2/3] tracing/hwlat: Don't ignore outer-loop duration when
 calculating max_latency

From: Srivatsa S. Bhat (VMware) <srivatsa@...il.mit.edu>

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.

Fixes: e7c15cd8a113 ("tracing: Added hardware latency tracer")
Cc: stable@...r.kernel.org
Signed-off-by: Srivatsa S. Bhat (VMware) <srivatsa@...il.mit.edu>
---

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

diff --git a/kernel/trace/trace_hwlat.c b/kernel/trace/trace_hwlat.c
index a0251a7..862f4b0 100644
--- a/kernel/trace/trace_hwlat.c
+++ b/kernel/trace/trace_hwlat.c
@@ -256,6 +256,8 @@ 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: