The following are examples of seeksize.d.

seeksize.d records disk head seek size for each operation by process.

This allows up to identify processes that are causing "random" disk

access and those causing "sequential" disk access.

It is desirable for processes to be accesing the disks in large

sequential operations. By using seeksize.d and bitesize.d we can

identify this behaviour.

In this example we read through a large file by copying it to a

remote server. Most of the seek sizes are zero, indicating sequential

access - and we would expect good performance from the disks

under these conditions,

# ./seeksize.d

Tracing... Hit Ctrl-C to end.

^C

22349 scp /dl/sol-10-b63-x86-v1.iso mars:\0

value ------------- Distribution ------------- count

-1 | 0

0 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 726

1 | 0

2 | 0

4 | 0

8 |@ 13

16 | 4

32 | 0

64 | 0

128 | 2

256 | 3

512 | 4

1024 | 4

2048 | 3

4096 | 0

8192 | 3

16384 | 0

32768 | 1

65536 | 0

In this example we run find. The disk operations are fairly scattered,

as illustrated below by the volume of non sequential reads,

# ./seeksize.d

Tracing... Hit Ctrl-C to end.

^C

22399 find /var/sadm/pkg/\0

value ------------- Distribution ------------- count

-1 | 0

0 |@@@@@@@@@@@@@ 1475

1 | 0

2 | 44

4 |@ 77

8 |@@@ 286

16 |@@ 191

32 |@ 154

64 |@@ 173

128 |@@ 179

256 |@@ 201

512 |@@ 186

1024 |@@ 236

2048 |@@ 201

4096 |@@ 274

8192 |@@ 243

16384 |@ 154

32768 |@ 113

65536 |@@ 182

131072 |@ 81

262144 | 0

I found the following interesting. This time I gzipp'd the large file.

While zipping, the process is reading from one location and writing

to another. One might expect that as the program toggles between

reading from one location and writing to another, that often the

distance would be the same (depending on where UFS puts the new file),

# ./seeksize.d

Tracing... Hit Ctrl-C to end.

^C

22368 gzip sol-10-b63-x86-v1.iso\0

value ------------- Distribution ------------- count

-1 | 0

0 |@@@@@@@@@@@@ 353

1 | 0

2 | 0

4 | 0

8 | 7

16 | 4

32 | 2

64 | 4

128 | 14

256 | 3

512 | 3

1024 | 5

2048 | 1

4096 | 0

8192 | 3

16384 | 1

32768 | 1

65536 | 1

131072 | 1

262144 |@@@@@@@@ 249

524288 | 1

1048576 | 2

2097152 | 1

4194304 | 2

8388608 |@@@@@@@@@@@@@@@@@@ 536

16777216 | 0

The following example compares the operation of "find" with "tar".

Both are reading from the same location, and we would expect that

both programs would generally need to do the same number of seeks

to navigate the direttory tree (depending on caching); and tar

causing extra operations as it reads the file contents as well,

# ./seeksize.d

Tracing... Hit Ctrl-C to end.

^C

PID CMD

22278 find /etc\0

value ------------- Distribution ------------- count

-1 | 0

0 |@@@@@@@@@@@@@@@@@@@@ 251

1 | 0

2 |@ 8

4 | 5

8 |@ 10

16 |@ 10

32 |@ 10

64 |@ 9

128 |@ 11

256 |@ 14

512 |@@ 20

1024 |@ 10

2048 | 6

4096 |@ 7

8192 |@ 10

16384 |@ 16

32768 |@@ 21

65536 |@@ 28

131072 |@ 7

262144 |@ 14

524288 | 6

1048576 |@ 15

2097152 |@ 7

4194304 | 0

22282 tar cf /dev/null /etc\0

value ------------- Distribution ------------- count

-1 | 0

0 |@@@@@@@@@@ 397

1 | 0

2 | 8

4 | 14

8 | 16

16 |@ 24

32 |@ 29

64 |@@ 99

128 |@@ 73

256 |@@ 78

512 |@@@ 109

1024 |@@ 62

2048 |@@ 69

4096 |@@ 73

8192 |@@@ 113

16384 |@@ 81

32768 |@@@ 111

65536 |@@@ 108

131072 |@ 49

262144 |@ 33

524288 | 20

1048576 | 13

2097152 | 7

4194304 | 5

8388608 |@ 30

16777216 | 0