Can you do me a favor?

Question

When you get the chance, run
$ ionice -c3 dd if=/dev/zero of=dumpfile bs=4096 count=1000000
And see what performance impact it has on your desktop. Note that -c3 indicates the process will get "idle" IO priority, which according to the ionice man page means this:
Idle A program running with idle I/O priority will only get disk time
when no other program has asked for disk I/O for a defined grace
period. The impact of an idle I/O process on normal system
activity should be zero. This scheduling class does not take a
priority argument. Presently, this scheduling class is permit‐
ted for an ordinary user (since kernel 2.6.25).
On my laptop, the dd process brings my system to a crawl even when ioniced to idle. Does that happen to anyone else?

Answer 1

This might be a situation where the GNU time, from extra/time, is more useful than bash's built-in.
$ /usr/bin/time -v ionice -c3 dd if=/dev/zero of=dumpfile bs=4096 count=1000000
1000000+0 records in
1000000+0 records out
4096000000 bytes (4.1 GB) copied, 38.545 s, 106 MB/s
Command being timed: "ionice -c3 dd if=/dev/zero of=dumpfile bs=4096 count=1000000"
User time (seconds): 0.14
System time (seconds): 8.92
Percent of CPU this job got: 22%
Elapsed (wall clock) time (h:mm:ss or m:ss): 0:39.51
Average shared text size (kbytes): 0
Average unshared data size (kbytes): 0
Average stack size (kbytes): 0
Average total size (kbytes): 0
Maximum resident set size (kbytes): 884
Average resident set size (kbytes): 0
Major (requiring I/O) page faults: 2
Minor (reclaiming a frame) page faults: 453
Voluntary context switches: 5947
Involuntary context switches: 1358
Swaps: 0
File system inputs: 64
File system outputs: 8000000
Socket messages sent: 0
Socket messages received: 0
Signals delivered: 0
Page size (bytes): 4096
Exit status: 0
Edit: Results without 'ionice -c3' are nearly identical:
$ /usr/bin/time -v dd if=/dev/zero of=dumpfile bs=4096 count=1000000
1000000+0 records in
1000000+0 records out
4096000000 bytes (4.1 GB) copied, 37.7916 s, 108 MB/s
Command being timed: "dd if=/dev/zero of=dumpfile bs=4096 count=1000000"
User time (seconds): 0.14
System time (seconds): 9.06
Percent of CPU this job got: 23%
Elapsed (wall clock) time (h:mm:ss or m:ss): 0:38.83
Average shared text size (kbytes): 0
Average unshared data size (kbytes): 0
Average stack size (kbytes): 0
Average total size (kbytes): 0
Maximum resident set size (kbytes): 884
Average resident set size (kbytes): 0
Major (requiring I/O) page faults: 2
Minor (reclaiming a frame) page faults: 272
Voluntary context switches: 7475
Involuntary context switches: 4398
Swaps: 0
File system inputs: 56
File system outputs: 8000000
Socket messages sent: 0
Socket messages received: 0
Signals delivered: 0
Page size (bytes): 4096
Exit status: 0
Last edited by thisoldman (2012-05-21 23:42:29)