ps and top give different CPU usage

I've seen a few posts similar to this, most notably here, but wasn't quite satisfied with the answers. I'm comparing top and ps results on a specific process and see huge discrepancies in CPU usage. top varies between <1% and 100% from interval to interval including periods of sustained highs (>50% for 3-4 intervals), while ps is steady at 2.2%. The process I'm watching doesn't have any children or anything, so I'm not quite sure what to make of it. Since there are sustained high periods in top, I feel I can rule out sampling interval.

Is this really just a discrepancy in how these two tools handle I/O wait time, as suggested by the question I linked to above?

EDIT:

I've seen it fluctuate to 2.1% in ps, but that's it so far. Output from top -p 4522:

PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND  

4522 root      16   0  340m 316m 4732 R 54.7  1.3 508:57.46 maui

Output from ps u -p 4522:

 USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND  

root      4522  2.2  1.3 348764 324456 ?       Ss   Aug25 509:25 /usr/local/maui/sbin/maui

edited Mar 20 '17 at 10:17

Community♦

asked Sep 10 '13 at 12:40

TTT

182214

You mean ps never ever changes and is always 2.2? Could you post the output of ps and top for the command in question so we can have a look?

– terdon
Sep 10 '13 at 13:18

@terdon I updated the original post with additional information.

– TTT
Sep 11 '13 at 13:16

add a comment |

Is this really just a discrepancy in how these two tools handle I/O wait time, as suggested by the question I linked to above?

EDIT:

I've seen it fluctuate to 2.1% in ps, but that's it so far. Output from top -p 4522:

PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND  

4522 root      16   0  340m 316m 4732 R 54.7  1.3 508:57.46 maui

Output from ps u -p 4522:

 USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND  

root      4522  2.2  1.3 348764 324456 ?       Ss   Aug25 509:25 /usr/local/maui/sbin/maui

edited Mar 20 '17 at 10:17

Community♦

asked Sep 10 '13 at 12:40

TTT

182214

You mean ps never ever changes and is always 2.2? Could you post the output of ps and top for the command in question so we can have a look?

– terdon
Sep 10 '13 at 13:18

@terdon I updated the original post with additional information.

– TTT
Sep 11 '13 at 13:16

add a comment |

Is this really just a discrepancy in how these two tools handle I/O wait time, as suggested by the question I linked to above?

EDIT:

I've seen it fluctuate to 2.1% in ps, but that's it so far. Output from top -p 4522:

PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND  

4522 root      16   0  340m 316m 4732 R 54.7  1.3 508:57.46 maui

Output from ps u -p 4522:

 USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND  

root      4522  2.2  1.3 348764 324456 ?       Ss   Aug25 509:25 /usr/local/maui/sbin/maui

edited Mar 20 '17 at 10:17

Community♦

asked Sep 10 '13 at 12:40

TTT

182214

Is this really just a discrepancy in how these two tools handle I/O wait time, as suggested by the question I linked to above?

EDIT:

I've seen it fluctuate to 2.1% in ps, but that's it so far. Output from top -p 4522:

PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND  

4522 root      16   0  340m 316m 4732 R 54.7  1.3 508:57.46 maui

Output from ps u -p 4522:

 USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND  

root      4522  2.2  1.3 348764 324456 ?       Ss   Aug25 509:25 /usr/local/maui/sbin/maui

linux top ps

edited Mar 20 '17 at 10:17

Community♦

asked Sep 10 '13 at 12:40

TTT

182214

edited Mar 20 '17 at 10:17

Community♦

asked Sep 10 '13 at 12:40

TTT

182214

edited Mar 20 '17 at 10:17

Community♦

edited Mar 20 '17 at 10:17

Community♦

edited Mar 20 '17 at 10:17

Community♦

asked Sep 10 '13 at 12:40

TTT

182214

asked Sep 10 '13 at 12:40

TTT

182214

asked Sep 10 '13 at 12:40

TTT

182214

You mean ps never ever changes and is always 2.2? Could you post the output of ps and top for the command in question so we can have a look?

– terdon
Sep 10 '13 at 13:18

@terdon I updated the original post with additional information.

– TTT
Sep 11 '13 at 13:16

add a comment |

You mean ps never ever changes and is always 2.2? Could you post the output of ps and top for the command in question so we can have a look?

– terdon
Sep 10 '13 at 13:18

@terdon I updated the original post with additional information.

– TTT
Sep 11 '13 at 13:16

You mean ps never ever changes and is always 2.2? Could you post the output of ps and top for the command in question so we can have a look?

– terdon
Sep 10 '13 at 13:18

@terdon I updated the original post with additional information.

– TTT
Sep 11 '13 at 13:16

add a comment |

2 Answers
2

active

oldest

votes

The likeliest reason is that top shows the percentage values as a percentage of a single CPU while ps shows the percentage of total available CPU power. Try running top and hitting ShiftI while it's running to show the percentage of all cores.

If this is a server cluster with a lot of CPUs, what you describe is normal behavior. Also see here.

edited Mar 20 '17 at 10:16

Community♦

answered Sep 11 '13 at 13:28

terdon

41.3k885135

Yes, I'm running on 12 cores. That does reduce the % levels that it reaches in top such that the average value is below that of ps, so that may be the difference. The process is a lot less active now, though, so it's hard to say...

– TTT
Sep 11 '13 at 15:48

1

@TTT this is a classic issue, it used to drive me up the wall before I discovered the shift+I thing.

– terdon
Sep 11 '13 at 17:18

add a comment |

This question is old, but in my opinion the answer is incorrect. ps and top calculates CPU usage using different methods.

from man top:

%CPU -- CPU Usage
The task's share of the elapsed CPU time since the last screen update, expressed as a percentage of total CPU time.

from man ps:

CPU usage is currently expressed as the percentage of time spent
running during the entire lifetime of a process.

So, lets say you have a process that was started a week ago and during that time it used 2.2% of CPU time on average. If suddenly it would became CPU intensive ( constantly consuming 100%) - looking at ps you would observe same 2.2% for the first few hours.

answered Jan 2 at 21:12

trukt

211

You're half-right in this case, since maui runs continuously in the background. But, even if ps and top averaged over the same time period, there'd still be a 12x difference because of the issue noted by the accepted answer. So, both answers are partially correct.

– TTT
Jan 12 at 15:25

add a comment |

Your Answer

StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "3"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);

StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});

function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});

}
});

draft saved

draft discarded

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fsuperuser.com%2fquestions%2f643331%2fps-and-top-give-different-cpu-usage%23new-answer', 'question_page');
}
);

Post as a guest

Name

Required, but never shown

2 Answers
2

active

oldest

votes

2 Answers
2

active

oldest

votes

If this is a server cluster with a lot of CPUs, what you describe is normal behavior. Also see here.

edited Mar 20 '17 at 10:16

Community♦

answered Sep 11 '13 at 13:28

terdon

41.3k885135

Yes, I'm running on 12 cores. That does reduce the % levels that it reaches in top such that the average value is below that of ps, so that may be the difference. The process is a lot less active now, though, so it's hard to say...

– TTT
Sep 11 '13 at 15:48

1

@TTT this is a classic issue, it used to drive me up the wall before I discovered the shift+I thing.

– terdon
Sep 11 '13 at 17:18

add a comment |

If this is a server cluster with a lot of CPUs, what you describe is normal behavior. Also see here.

edited Mar 20 '17 at 10:16

Community♦

answered Sep 11 '13 at 13:28

terdon

41.3k885135

Yes, I'm running on 12 cores. That does reduce the % levels that it reaches in top such that the average value is below that of ps, so that may be the difference. The process is a lot less active now, though, so it's hard to say...

– TTT
Sep 11 '13 at 15:48

1

@TTT this is a classic issue, it used to drive me up the wall before I discovered the shift+I thing.

– terdon
Sep 11 '13 at 17:18

add a comment |

If this is a server cluster with a lot of CPUs, what you describe is normal behavior. Also see here.

edited Mar 20 '17 at 10:16

Community♦

answered Sep 11 '13 at 13:28

terdon

41.3k885135

If this is a server cluster with a lot of CPUs, what you describe is normal behavior. Also see here.

edited Mar 20 '17 at 10:16

Community♦

answered Sep 11 '13 at 13:28

terdon

41.3k885135

edited Mar 20 '17 at 10:16

Community♦

edited Mar 20 '17 at 10:16

Community♦

edited Mar 20 '17 at 10:16

Community♦

answered Sep 11 '13 at 13:28

terdon

41.3k885135

answered Sep 11 '13 at 13:28

terdon

41.3k885135

answered Sep 11 '13 at 13:28

terdon

41.3k885135

Yes, I'm running on 12 cores. That does reduce the % levels that it reaches in top such that the average value is below that of ps, so that may be the difference. The process is a lot less active now, though, so it's hard to say...

– TTT
Sep 11 '13 at 15:48

1

@TTT this is a classic issue, it used to drive me up the wall before I discovered the shift+I thing.

– terdon
Sep 11 '13 at 17:18

add a comment |

Yes, I'm running on 12 cores. That does reduce the % levels that it reaches in top such that the average value is below that of ps, so that may be the difference. The process is a lot less active now, though, so it's hard to say...

– TTT
Sep 11 '13 at 15:48

1

@TTT this is a classic issue, it used to drive me up the wall before I discovered the shift+I thing.

– terdon
Sep 11 '13 at 17:18

Yes, I'm running on 12 cores. That does reduce the % levels that it reaches in top such that the average value is below that of ps, so that may be the difference. The process is a lot less active now, though, so it's hard to say...

– TTT
Sep 11 '13 at 15:48

@TTT this is a classic issue, it used to drive me up the wall before I discovered the shift+I thing.

– terdon
Sep 11 '13 at 17:18

add a comment |

This question is old, but in my opinion the answer is incorrect. ps and top calculates CPU usage using different methods.

from man top:

%CPU -- CPU Usage
The task's share of the elapsed CPU time since the last screen update, expressed as a percentage of total CPU time.

from man ps:

CPU usage is currently expressed as the percentage of time spent
running during the entire lifetime of a process.

answered Jan 2 at 21:12

trukt

211

You're half-right in this case, since maui runs continuously in the background. But, even if ps and top averaged over the same time period, there'd still be a 12x difference because of the issue noted by the accepted answer. So, both answers are partially correct.

– TTT
Jan 12 at 15:25

add a comment |

This question is old, but in my opinion the answer is incorrect. ps and top calculates CPU usage using different methods.

from man top:

%CPU -- CPU Usage
The task's share of the elapsed CPU time since the last screen update, expressed as a percentage of total CPU time.

from man ps:

CPU usage is currently expressed as the percentage of time spent
running during the entire lifetime of a process.

answered Jan 2 at 21:12

trukt

211

You're half-right in this case, since maui runs continuously in the background. But, even if ps and top averaged over the same time period, there'd still be a 12x difference because of the issue noted by the accepted answer. So, both answers are partially correct.

– TTT
Jan 12 at 15:25

add a comment |

This question is old, but in my opinion the answer is incorrect. ps and top calculates CPU usage using different methods.

from man top:

%CPU -- CPU Usage
The task's share of the elapsed CPU time since the last screen update, expressed as a percentage of total CPU time.

from man ps:

CPU usage is currently expressed as the percentage of time spent
running during the entire lifetime of a process.

answered Jan 2 at 21:12

trukt

211

This question is old, but in my opinion the answer is incorrect. ps and top calculates CPU usage using different methods.

from man top:

%CPU -- CPU Usage
The task's share of the elapsed CPU time since the last screen update, expressed as a percentage of total CPU time.

from man ps:

CPU usage is currently expressed as the percentage of time spent
running during the entire lifetime of a process.

answered Jan 2 at 21:12

trukt

211

answered Jan 2 at 21:12

trukt

211

answered Jan 2 at 21:12

trukt

211

answered Jan 2 at 21:12

trukt

211

You're half-right in this case, since maui runs continuously in the background. But, even if ps and top averaged over the same time period, there'd still be a 12x difference because of the issue noted by the accepted answer. So, both answers are partially correct.

– TTT
Jan 12 at 15:25

add a comment |

You're half-right in this case, since maui runs continuously in the background. But, even if ps and top averaged over the same time period, there'd still be a 12x difference because of the issue noted by the accepted answer. So, both answers are partially correct.

– TTT
Jan 12 at 15:25

You're half-right in this case, since maui runs continuously in the background. But, even if ps and top averaged over the same time period, there'd still be a 12x difference because of the issue noted by the accepted answer. So, both answers are partially correct.

– TTT
Jan 12 at 15:25

add a comment |

draft saved

draft discarded

Thanks for contributing an answer to Super User!

Please be sure to answer the question. Provide details and share your research!

But avoid …

Asking for help, clarification, or responding to other answers.

Making statements based on opinion; back them up with references or personal experience.

To learn more, see our tips on writing great answers.

draft saved

draft discarded

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Post as a guest

Name

Required, but never shown

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Name

Required, but never shown

Name

Required, but never shown

This page is only for reference, If you need detailed information, please check here

搜尋此網誌

Jtdylktuy