-
Notifications
You must be signed in to change notification settings - Fork 3.9k
/
runqlen_example.txt
295 lines (243 loc) · 11.9 KB
/
runqlen_example.txt
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
Demonstrations of runqlen, the Linux eBPF/bcc version.
This program summarizes scheduler queue length as a histogram, and can also
show run queue occupancy. It works by sampling the run queue length on all
CPUs at 99 Hertz.
As an example, here is an idle system:
# ./runqlen.py
Sampling run queue length... Hit Ctrl-C to end.
^C
runqlen : count distribution
0 : 1776 |****************************************|
This shows a zero run queue length each time it was sampled.
And now a heavily loaded system:
# ./runqlen.py
Sampling run queue length... Hit Ctrl-C to end.
^C
runqlen : count distribution
0 : 1068 |****************************************|
1 : 642 |************************ |
2 : 369 |************* |
3 : 183 |****** |
4 : 104 |*** |
5 : 42 |* |
6 : 13 | |
7 : 2 | |
8 : 1 | |
Now there is often threads queued, with one sample reaching a queue length
of 8. This will cause run queue latency, which can be measured by the bcc
runqlat tool.
Here's an example of an issue that runqlen can identify. Starting with the
system-wide summary:
# ./runqlen.py
Sampling run queue length... Hit Ctrl-C to end.
^C
runqlen : count distribution
0 : 1209 |****************************************|
1 : 372 |************ |
2 : 73 |** |
3 : 3 | |
4 : 1 | |
5 : 0 | |
6 : 0 | |
7 : 237 |******* |
This shows there is often a run queue length of 7. Now using the -C option to
see per-CPU histograms:
# ./runqlen.py -C
Sampling run queue length... Hit Ctrl-C to end.
^C
cpu = 0
runqlen : count distribution
0 : 257 |****************************************|
1 : 64 |********* |
2 : 5 | |
3 : 0 | |
4 : 0 | |
5 : 0 | |
6 : 1 | |
cpu = 1
runqlen : count distribution
0 : 226 |****************************************|
1 : 90 |*************** |
2 : 11 |* |
cpu = 2
runqlen : count distribution
0 : 264 |****************************************|
1 : 52 |******* |
2 : 8 |* |
3 : 1 | |
4 : 0 | |
5 : 0 | |
6 : 1 | |
7 : 0 | |
8 : 1 | |
cpu = 3
runqlen : count distribution
0 : 0 | |
1 : 0 | |
2 : 0 | |
3 : 0 | |
4 : 0 | |
5 : 0 | |
6 : 0 | |
7 : 327 |****************************************|
cpu = 4
runqlen : count distribution
0 : 255 |****************************************|
1 : 63 |********* |
2 : 9 |* |
cpu = 5
runqlen : count distribution
0 : 244 |****************************************|
1 : 78 |************ |
2 : 3 | |
3 : 2 | |
cpu = 6
runqlen : count distribution
0 : 253 |****************************************|
1 : 66 |********** |
2 : 6 | |
3 : 1 | |
4 : 1 | |
cpu = 7
runqlen : count distribution
0 : 243 |****************************************|
1 : 74 |************ |
2 : 6 | |
3 : 1 | |
4 : 0 | |
5 : 1 | |
6 : 2 | |
The run queue length of 7 is isolated to CPU 3. It was caused by CPU binding
(taskset). This can sometimes happen by applications that try to auto-bind
to CPUs, leaving other CPUs idle while work is queued.
runqlat accepts an interval and a count. For example, with -T for timestamps:
# ./runqlen.py -T 1 5
Sampling run queue length... Hit Ctrl-C to end.
19:51:34
runqlen : count distribution
0 : 635 |****************************************|
1 : 142 |******** |
2 : 13 | |
3 : 0 | |
4 : 1 | |
19:51:35
runqlen : count distribution
0 : 640 |****************************************|
1 : 136 |******** |
2 : 13 | |
3 : 1 | |
4 : 0 | |
5 : 0 | |
6 : 0 | |
7 : 0 | |
8 : 0 | |
9 : 0 | |
10 : 1 | |
19:51:36
runqlen : count distribution
0 : 603 |****************************************|
1 : 170 |*********** |
2 : 16 |* |
3 : 1 | |
4 : 0 | |
5 : 0 | |
6 : 0 | |
7 : 0 | |
8 : 0 | |
9 : 1 | |
19:51:37
runqlen : count distribution
0 : 617 |****************************************|
1 : 154 |********* |
2 : 20 |* |
3 : 0 | |
4 : 0 | |
5 : 0 | |
6 : 0 | |
7 : 0 | |
8 : 0 | |
9 : 0 | |
10 : 0 | |
11 : 1 | |
19:51:38
runqlen : count distribution
0 : 603 |****************************************|
1 : 161 |********** |
2 : 24 |* |
3 : 4 | |
The spikes in run queue length of 11 are likely threads waking up at the same
time (a thundering herd), and then are scheduled and complete their execution
quickly.
The -O option prints run queue occupancy: the percentage of time that there
was work queued waiting its turn. Eg:
# ./runqlen.py -OT 1
Sampling run queue length... Hit Ctrl-C to end.
19:54:53
runqocc: 41.09%
19:54:54
runqocc: 41.85%
19:54:55
runqocc: 41.47%
19:54:56
runqocc: 42.35%
19:54:57
runqocc: 40.83%
[...]
This can also be examined per-CPU:
# ./runqlen.py -COT 1
Sampling run queue length... Hit Ctrl-C to end.
19:55:03
runqocc, CPU 0 32.32%
runqocc, CPU 1 26.26%
runqocc, CPU 2 38.38%
runqocc, CPU 3 100.00%
runqocc, CPU 4 26.26%
runqocc, CPU 5 32.32%
runqocc, CPU 6 39.39%
runqocc, CPU 7 46.46%
19:55:04
runqocc, CPU 0 35.00%
runqocc, CPU 1 32.32%
runqocc, CPU 2 37.00%
runqocc, CPU 3 100.00%
runqocc, CPU 4 43.43%
runqocc, CPU 5 31.31%
runqocc, CPU 6 28.00%
runqocc, CPU 7 31.31%
19:55:05
runqocc, CPU 0 43.43%
runqocc, CPU 1 32.32%
runqocc, CPU 2 45.45%
runqocc, CPU 3 100.00%
runqocc, CPU 4 29.29%
runqocc, CPU 5 36.36%
runqocc, CPU 6 36.36%
runqocc, CPU 7 30.30%
19:55:06
runqocc, CPU 0 40.00%
runqocc, CPU 1 38.00%
runqocc, CPU 2 31.31%
runqocc, CPU 3 100.00%
runqocc, CPU 4 31.31%
runqocc, CPU 5 28.28%
runqocc, CPU 6 31.00%
runqocc, CPU 7 29.29%
[...]
USAGE message:
# ./runqlen -h
usage: runqlen [-h] [-T] [-O] [-C] [interval] [count]
Summarize scheduler run queue length as a histogram
positional arguments:
interval output interval, in seconds
count number of outputs
optional arguments:
-h, --help show this help message and exit
-T, --timestamp include timestamp on output
-O, --runqocc report run queue occupancy
-C, --cpus print output for each CPU separately
examples:
./runqlen # summarize run queue length as a histogram
./runqlen 1 10 # print 1 second summaries, 10 times
./runqlen -T 1 # 1s summaries and timestamps
./runqlen -O # report run queue occupancy
./runqlen -C # show each CPU separately