forked from iovisor/bcc
/
biolatency_example.txt
321 lines (270 loc) · 16.8 KB
/
biolatency_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
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
Demonstrations of biolatency, the Linux eBPF/bcc version.
biolatency traces block device I/O (disk I/O), and records the distribution
of I/O latency (time), printing this as a histogram when Ctrl-C is hit.
For example:
# ./biolatency
Tracing block device I/O... Hit Ctrl-C to end.
^C
usecs : count distribution
0 -> 1 : 0 | |
2 -> 3 : 0 | |
4 -> 7 : 0 | |
8 -> 15 : 0 | |
16 -> 31 : 0 | |
32 -> 63 : 0 | |
64 -> 127 : 1 | |
128 -> 255 : 12 |******** |
256 -> 511 : 15 |********** |
512 -> 1023 : 43 |******************************* |
1024 -> 2047 : 52 |**************************************|
2048 -> 4095 : 47 |********************************** |
4096 -> 8191 : 52 |**************************************|
8192 -> 16383 : 36 |************************** |
16384 -> 32767 : 15 |********** |
32768 -> 65535 : 2 |* |
65536 -> 131071 : 2 |* |
The latency of the disk I/O is measured from the issue to the device to its
completion. A -Q option can be used to include time queued in the kernel.
This example output shows a large mode of latency from about 128 microseconds
to about 32767 microseconds (33 milliseconds). The bulk of the I/O was
between 1 and 8 ms, which is the expected block device latency for
rotational storage devices.
The highest latency seen while tracing was between 65 and 131 milliseconds:
the last row printed, for which there were 2 I/O.
For efficiency, biolatency uses an in-kernel eBPF map to store timestamps
with requests, and another in-kernel map to store the histogram (the "count")
column, which is copied to user-space only when output is printed. These
methods lower the performance overhead when tracing is performed.
In the following example, the -m option is used to print a histogram using
milliseconds as the units (which eliminates the first several rows), -T to
print timestamps with the output, and to print 1 second summaries 5 times:
# ./biolatency -mT 1 5
Tracing block device I/O... Hit Ctrl-C to end.
06:20:16
msecs : count distribution
0 -> 1 : 36 |**************************************|
2 -> 3 : 1 |* |
4 -> 7 : 3 |*** |
8 -> 15 : 17 |***************** |
16 -> 31 : 33 |********************************** |
32 -> 63 : 7 |******* |
64 -> 127 : 6 |****** |
06:20:17
msecs : count distribution
0 -> 1 : 96 |************************************ |
2 -> 3 : 25 |********* |
4 -> 7 : 29 |*********** |
8 -> 15 : 62 |*********************** |
16 -> 31 : 100 |**************************************|
32 -> 63 : 62 |*********************** |
64 -> 127 : 18 |****** |
06:20:18
msecs : count distribution
0 -> 1 : 68 |************************* |
2 -> 3 : 76 |**************************** |
4 -> 7 : 20 |******* |
8 -> 15 : 48 |***************** |
16 -> 31 : 103 |**************************************|
32 -> 63 : 49 |****************** |
64 -> 127 : 17 |****** |
06:20:19
msecs : count distribution
0 -> 1 : 522 |*************************************+|
2 -> 3 : 225 |**************** |
4 -> 7 : 38 |** |
8 -> 15 : 8 | |
16 -> 31 : 1 | |
06:20:20
msecs : count distribution
0 -> 1 : 436 |**************************************|
2 -> 3 : 106 |********* |
4 -> 7 : 34 |** |
8 -> 15 : 19 |* |
16 -> 31 : 1 | |
How the I/O latency distribution changes over time can be seen.
The -Q option begins measuring I/O latency from when the request was first
queued in the kernel, and includes queuing latency:
# ./biolatency -Q
Tracing block device I/O... Hit Ctrl-C to end.
^C
usecs : count distribution
0 -> 1 : 0 | |
2 -> 3 : 0 | |
4 -> 7 : 0 | |
8 -> 15 : 0 | |
16 -> 31 : 0 | |
32 -> 63 : 0 | |
64 -> 127 : 0 | |
128 -> 255 : 3 |* |
256 -> 511 : 37 |************** |
512 -> 1023 : 30 |*********** |
1024 -> 2047 : 18 |******* |
2048 -> 4095 : 22 |******** |
4096 -> 8191 : 14 |***** |
8192 -> 16383 : 48 |******************* |
16384 -> 32767 : 96 |**************************************|
32768 -> 65535 : 31 |************ |
65536 -> 131071 : 26 |********** |
131072 -> 262143 : 12 |**** |
This better reflects the latency suffered by the application (if it is
synchronous I/O), whereas the default mode without kernel queueing better
reflects the performance of the device.
Note that the storage device (and storage device controller) usually have
queues of their own, which are always included in the latency, with or
without -Q.
The -D option will print a histogram per disk. Eg:
# ./biolatency -D
Tracing block device I/O... Hit Ctrl-C to end.
^C
Bucket disk = 'xvdb'
usecs : count distribution
0 -> 1 : 0 | |
2 -> 3 : 0 | |
4 -> 7 : 0 | |
8 -> 15 : 0 | |
16 -> 31 : 0 | |
32 -> 63 : 0 | |
64 -> 127 : 0 | |
128 -> 255 : 1 | |
256 -> 511 : 33 |********************** |
512 -> 1023 : 36 |************************ |
1024 -> 2047 : 58 |****************************************|
2048 -> 4095 : 51 |*********************************** |
4096 -> 8191 : 21 |************** |
8192 -> 16383 : 2 |* |
Bucket disk = 'xvdc'
usecs : count distribution
0 -> 1 : 0 | |
2 -> 3 : 0 | |
4 -> 7 : 0 | |
8 -> 15 : 0 | |
16 -> 31 : 0 | |
32 -> 63 : 0 | |
64 -> 127 : 0 | |
128 -> 255 : 1 | |
256 -> 511 : 38 |*********************** |
512 -> 1023 : 42 |************************* |
1024 -> 2047 : 66 |****************************************|
2048 -> 4095 : 40 |************************ |
4096 -> 8191 : 14 |******** |
Bucket disk = 'xvda1'
usecs : count distribution
0 -> 1 : 0 | |
2 -> 3 : 0 | |
4 -> 7 : 0 | |
8 -> 15 : 0 | |
16 -> 31 : 0 | |
32 -> 63 : 0 | |
64 -> 127 : 0 | |
128 -> 255 : 0 | |
256 -> 511 : 18 |********** |
512 -> 1023 : 67 |************************************* |
1024 -> 2047 : 35 |******************* |
2048 -> 4095 : 71 |****************************************|
4096 -> 8191 : 65 |************************************ |
8192 -> 16383 : 65 |************************************ |
16384 -> 32767 : 20 |*********** |
32768 -> 65535 : 7 |*** |
This output sows that xvda1 has much higher latency, usually between 0.5 ms
and 32 ms, whereas xvdc is usually between 0.2 ms and 4 ms.
The -F option prints a separate histogram for each unique set of request
flags. For example:
./biolatency.py -Fm
Tracing block device I/O... Hit Ctrl-C to end.
^C
flags = Read
msecs : count distribution
0 -> 1 : 180 |************* |
2 -> 3 : 519 |****************************************|
4 -> 7 : 60 |**** |
8 -> 15 : 123 |********* |
16 -> 31 : 68 |***** |
32 -> 63 : 0 | |
64 -> 127 : 2 | |
128 -> 255 : 12 | |
256 -> 511 : 0 | |
512 -> 1023 : 1 | |
flags = Sync-Write
msecs : count distribution
0 -> 1 : 5 |****************************************|
flags = Flush
msecs : count distribution
0 -> 1 : 2 |****************************************|
flags = Metadata-Read
msecs : count distribution
0 -> 1 : 3 |****************************************|
2 -> 3 : 2 |************************** |
4 -> 7 : 0 | |
8 -> 15 : 1 |************* |
16 -> 31 : 1 |************* |
flags = Write
msecs : count distribution
0 -> 1 : 103 |******************************* |
2 -> 3 : 106 |******************************** |
4 -> 7 : 130 |****************************************|
8 -> 15 : 79 |************************ |
16 -> 31 : 5 |* |
32 -> 63 : 0 | |
64 -> 127 : 0 | |
128 -> 255 : 0 | |
256 -> 511 : 1 | |
flags = NoMerge-Read
msecs : count distribution
0 -> 1 : 0 | |
2 -> 3 : 5 |****************************************|
4 -> 7 : 0 | |
8 -> 15 : 0 | |
16 -> 31 : 1 |******** |
flags = NoMerge-Write
msecs : count distribution
0 -> 1 : 30 |** |
2 -> 3 : 293 |******************** |
4 -> 7 : 564 |****************************************|
8 -> 15 : 463 |******************************** |
16 -> 31 : 21 |* |
32 -> 63 : 0 | |
64 -> 127 : 0 | |
128 -> 255 : 0 | |
256 -> 511 : 5 | |
flags = Priority-Metadata-Read
msecs : count distribution
0 -> 1 : 1 |****************************************|
2 -> 3 : 0 | |
4 -> 7 : 1 |****************************************|
8 -> 15 : 1 |****************************************|
flags = ForcedUnitAccess-Metadata-Sync-Write
msecs : count distribution
0 -> 1 : 2 |****************************************|
flags = ReadAhead-Read
msecs : count distribution
0 -> 1 : 15 |*************************** |
2 -> 3 : 22 |****************************************|
4 -> 7 : 14 |************************* |
8 -> 15 : 8 |************** |
16 -> 31 : 1 |* |
flags = Priority-Metadata-Write
msecs : count distribution
0 -> 1 : 9 |****************************************|
These can be handled differently by the storage device, and this mode lets us
examine their performance in isolation.
USAGE message:
# ./biolatency -h
usage: biolatency [-h] [-T] [-Q] [-m] [-D] [-F] [interval] [count]
Summarize block device I/O latency 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
-Q, --queued include OS queued time in I/O time
-m, --milliseconds millisecond histogram
-D, --disks print a histogram per disk device
-F, --flags print a histogram per set of I/O flags
examples:
./biolatency # summarize block I/O latency as a histogram
./biolatency 1 10 # print 1 second summaries, 10 times
./biolatency -mT 1 # 1s summaries, milliseconds, and timestamps
./biolatency -Q # include OS queued time in I/O time
./biolatency -D # show each disk device separately
./biolatency -F # show I/O flags separately