Messages in this thread | | | Date | Mon, 18 Jan 2016 17:59:46 +0000 | From | Mel Gorman <> | Subject | perf stat stddev reporting broken since "perf stat: Introduce read_counters function" |
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I noticed that perf stat in 4.4 is not printing stddev figures as expected and bisected it to commit 106a94a0f8c2 ("perf stat: Introduce read_counters function").
# Kernel 4.4 # make clean && make prefix=/usr && ./perf stat -r 5 sleep 1 Performance counter stats for 'sleep 1' (5 runs):
0.466683 task-clock (msec) # 0.000 CPUs utilized 1 context-switches # 0.002 M/sec 1 cpu-migrations # 0.002 M/sec 66 page-faults # 0.144 M/sec 1,630,220 cycles # 3.562 GHz <not supported> stalled-cycles-frontend <not supported> stalled-cycles-backend 902,686 instructions # 0.66 insns per cycle 185,692 branches # 405.786 M/sec 8,640 branch-misses # 4.63% of all branches
1.000855883 seconds time elapsed ( +- 0.01% )
# git checkout 106a94a0f8c207ef4113ce7e32f34a00b3b174e7^ Performance counter stats for 'sleep 1' (5 runs):
0.397939 task-clock (msec) # 0.000 CPUs utilized ( +- 3.37% ) 1 context-switches # 0.003 M/sec 0 cpu-migrations # 0.000 K/sec 67 page-faults # 0.169 M/sec ( +- 0.56% ) 1,360,763 cycles # 3.420 GHz ( +- 2.14% ) <not supported> stalled-cycles-frontend <not supported> stalled-cycles-backend 903,901 instructions # 0.66 insns per cycle ( +- 0.24% ) 186,472 branches # 468.595 M/sec ( +- 0.29% ) 8,599 branch-misses # 4.61% of all branches ( +- 0.77% )
1.000761882 seconds time elapsed ( +- 0.00% )
# git checkout 106a94a0f8c207ef4113ce7e32f34a00b3b174e7
Performance counter stats for 'sleep 1' (5 runs):
0.583178 task-clock (msec) # 0.001 CPUs utilized 1 context-switches # 0.002 M/sec 0 cpu-migrations # 0.000 K/sec 67 page-faults # 0.141 M/sec 1,224,416 cycles # 2.585 GHz <not supported> stalled-cycles-frontend <not supported> stalled-cycles-backend 892,568 instructions # 0.68 insns per cycle 184,975 branches # 390.554 M/sec 8,512 branch-misses # 4.57% of all branches
1.000889249 seconds time elapsed ( +- 0.01% )
I checked and current master in Linus' tree is also broken. Is this change in documented perf stat behaviour intentional?
-- Mel Gorman SUSE Labs
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