On 06/24/2015 10:46 AM, Ingo Molnar wrote:
> So I'd suggest to first compare preemption behavior: does the workload
> context-switch heavily, and is it the exact same context switching rate and
> are
> the points of preemption the same as well between the two kernels?
If I read this correctly, the answer is yes.
First the 'stable' flock02 test:
perf stat --repeat 5 --pre 'rm -rf /tmp/a' ~/src/lockperf/flock02 -n 128 -l 64
/tmp/a
0.008793148
0.008784990
0.008587804
0.008693641
0.008776946
Performance counter stats for '/home/wagi/src/lockperf/flock02 -n 128 -l 64
/tmp/a' (5 runs):
76.509634 task-clock (msec) # 3.312 CPUs utilized
( +- 0.67% )
2 context-switches # 0.029 K/sec
( +- 26.50% )
128 cpu-migrations # 0.002 M/sec
( +- 0.31% )
5,295 page-faults # 0.069 M/sec
( +- 0.49% )
89,944,154 cycles # 1.176 GHz
( +- 0.66% )
58,670,259 stalled-cycles-frontend # 65.23% frontend cycles
idle ( +- 0.88% )
0 stalled-cycles-backend # 0.00% backend cycles
idle
76,991,414 instructions # 0.86 insns per cycle
# 0.76 stalled cycles per
insn ( +- 0.19% )
15,239,720 branches # 199.187 M/sec
( +- 0.20% )
103,418 branch-misses # 0.68% of all branches
( +- 6.68% )
0.023102895 seconds time elapsed
( +- 1.09% )
And here posix01 which shows high variance:
perf stat --repeat 5 --pre 'rm -rf /tmp/a' ~/src/lockperf/posix01 -n 128 -l 64
/tmp/a
0.006020402
32.510838421
55.516466069
46.794470223
5.097701438
Performance counter stats for '/home/wagi/src/lockperf/posix01 -n 128 -l 64
/tmp/a' (5 runs):
4177.932106 task-clock (msec) # 14.162 CPUs utilized
( +- 34.59% )
70,646 context-switches # 0.017 M/sec
( +- 31.56% )
28,009 cpu-migrations # 0.007 M/sec
( +- 33.55% )
4,834 page-faults # 0.001 M/sec
( +- 0.98% )
7,291,160,968 cycles # 1.745 GHz
( +- 32.17% )
5,216,204,262 stalled-cycles-frontend # 71.54% frontend cycles
idle ( +- 32.13% )
0 stalled-cycles-backend # 0.00% backend cycles
idle
1,901,289,780 instructions # 0.26 insns per cycle
# 2.74 stalled cycles per
insn ( +- 30.80% )
440,415,914 branches # 105.415 M/sec
( +- 31.06% )
1,347,021 branch-misses # 0.31% of all branches
( +- 29.17% )
0.295016987 seconds time elapsed
( +- 32.01% )
BTW, thanks for the perf stat tip. Really handy!
cheers,
daniel
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