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2ced5853b4
lshwc displays counter values extracted from the /dev/hwctr device.
The counter values are retrieved using a loop and incremented instead
of just displayed on output.
This leads to the situation where a counter is incremented in large
numbers while the counter triggering program is active. When this
program terminates, the counter should not increase but remain steady.
This is not the case as this example shows:
# lshwc -i 2 -l90 -a :a | fgrep Total | \
awk -F ',' '{print $2 "," $152 "," $157}'
Report time and values of DFLT_ACCESS and DFLT_CC counters
sleep 10
# DFLTCC=1 python3 -c "import zlib; zlib.compress(b'A'*6000000000);
Increment counter DFLT_ACCESS and DFLT_CC, runs about 45 seconds
Output before:
15:24:20,0,0
15:24:22,0,0
15:24:24,0,0
15:24:26,0,0
15:24:28,0,0
15:24:30,0,0
15:24:32,2067027,592996481 <--- python3 program start
15:24:34,6953101,2039012580
15:24:36,14494585,4264340060
15:24:38,24759568,7346128396
....
15:24:56,232929262,70526362509
15:24:58,269037963,81464038124
15:25:00,307757248,93171809261
15:25:02,348900718,105620730492
15:25:04,392646075,118841031269 <--- python3 program stop
15:25:06,438956016,132853968029 <-- Value column two increased by 49148217
15:25:08,488104233,147709011658 <-- Similar high increase
The reason is that lshwc takes the last read counter value and keeps
adding it to the total count, even if there zero delta to the previous
read value. Fix this by clearing the total count value between ioctl()
read operations.
Output after:
15:39:26,0,0
15:39:28,0,0
15:39:30,0,0
15:39:32,0,0
15:39:34,0,0
15:39:36,1367250,380721127 <--- python3 program start
15:39:38,4104791,1108181711
15:39:40,6740994,1858843730
15:39:42,9277545,2646351211
15:39:44,11895180,3444375804
....
15:40:16,54060774,16315924126
15:40:18,57830349,17513712210
15:40:20,61628170,18690791102
15:40:22,65410470,19864086006
15:40:24,69070765,21028646754 <--- python3 program stop
15:40:26,70429758,21472772340 <-- No increase of value in column two
15:40:28,70429758,21472772340
15:40:30,70429758,21472772340
15:40:32,70429758,21472772340
15:40:34,70429758,21472772340
15:40:36,70429758,21472772340
15:40:38,70429758,21472772340
Fixes: 27a562da0a ("cpumf/lshwc: Program to extract complete counter sets")
Reported-by: Axel Busch <Axel.Busch@ibm.com>
Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
Acked-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>