linux-kernel - [PATCH 1/3] tracing/hwlat: Report total time spent in all NMIs during the sample

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Date:   Thu, 10 Oct 2019 11:50:46 -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 1/3] tracing/hwlat: Report total time spent in all NMIs
 during the sample

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

nmi_total_ts is supposed to record the total time spent in *all* NMIs
that occur on the given CPU during the (active portion of the)
sampling window. However, the code seems to be overwriting this
variable for each NMI, thereby only recording the time spent in the
most recent NMI. Fix it by accumulating the duration instead.

Fixes: 7b2c86250122 ("tracing: Add NMI tracing in hwlat detector")
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, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/trace_hwlat.c b/kernel/trace/trace_hwlat.c
index fa95139..a0251a7 100644
--- a/kernel/trace/trace_hwlat.c
+++ b/kernel/trace/trace_hwlat.c
@@ -150,7 +150,7 @@ void trace_hwlat_callback(bool enter)
 		if (enter)
 			nmi_ts_start = time_get();
 		else
-			nmi_total_ts = time_get() - nmi_ts_start;
+			nmi_total_ts += time_get() - nmi_ts_start;
 	}
 
 	if (enter)