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nicotine

Member

Registered: 2015-10-07

Posts: 5

xfce4-taskmanager using lots of cpu

Hi,

I am currently administering a few Dell servers: Poweredge 730.
I am running Ubuntu 14.04 LTS with 'Xubuntu' (= xfce).
These systems heve 2 cpu's with 12 cores each, so total 24 cores (48 if you count hyper-threading)

On this system I have a problem with xfce4-taskmager. It gives conflicting numbers compared to top with respect to CPU usage.

according to top, xfce4-taskmager uses 32% CPU. According to task-manager itself it uses only 1%.
According to top, top uses 0.7% CPU, according to task-manager it is 0%.

Now I am inclined to believe top.

Could it be that there is something inefficient and wrong about task-manager? because 32% is clearly to much.
BTW I use the default refresh of .75 s. If I decrease the refresh CPU usages goes down but is still far
higher then top with a 1 s. refresh

Regards,
Nico

ToZ

Administrator

From: Canada

Registered: 2011-06-02

Posts: 11,494

Re: xfce4-taskmanager using lots of cpu

Just had a look and noticed this as well. However, if I turn off Irix mode in top (I) I then get consistent readings between the two. Further investigation led me to http://unix.stackexchange.com/questions … op-command and from my top man page:

1. %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.

           In a true SMP environment, if a process is multi-threaded  and
           top  is  not  operating  in Threads mode, amounts greater than
           100% may be reported.  You toggle Threads mode  with  the  `H'
           interactive command.

           Also  for  multi-processor  environments, if Irix mode is Off,
           top will operate in Solaris mode where a task's cpu usage will
           be   divided   by  the  total  number  of  CPUs.   You  toggle
           Irix/Solaris modes with the `I' interactive command.

So I guess, xfce4-taskmanager is calculating the numbers as an overall percentage of all CPUs where top (by default) calculates it per CPU.

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nicotine

Member

Registered: 2015-10-07

Posts: 5

Re: xfce4-taskmanager using lots of cpu

Right. I was already thinking along the same lines just now.

But note that this will explain the differences in CPU usage as REPORTED by top and task-manager,
but not the fact that task-manger is actually using 32% versus 1% for top (as reported by top).

nicotine

Member

Registered: 2015-10-07

Posts: 5

Re: xfce4-taskmanager using lots of cpu

I also tried xfce4-taskmanager om my opensuse 13.2 desktop wich has 8 I7 cores.
Based on a 1 s. refresh I get (as measured by top) roughly 4% for 8 cores and 24% for 24 cores.
Now this is not a linear increase as one might hope.
It look like there is a possibility for a quadratic increase in CPU load. Something that will 'explode' as you increase the number of cores further.

Is there a possibility to attract the attention of a developer for this issue?

ToZ

Administrator

From: Canada

Registered: 2011-06-02

Posts: 11,494

Re: xfce4-taskmanager using lots of cpu

Is there a possibility to attract the attention of a developer for this issue?

The best way is to file a bug report. Other channels include the xfce4-dev mailing list and the #xfce IRC channel on freenode.

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MountainDewManiac

Member

From: Where Mr. Bankruptcy is Prez

Registered: 2013-03-24

Posts: 1,115

Re: xfce4-taskmanager using lots of cpu

That'd be a good subject for discussion on the mailing list, IMO. You could quickly (one assumes) find out if there is an error in reporting, if it is some sort of misunderstanding (IOW, if it is reporting the figure based on something else such as, IDK, a percentage of the whole workload instead of a percentage of the capacity or something?), or if the app is actually using "grossly" more CPU capacity as the amount of cores/etc. increase.

BtW, 24% on a 24-core system would seem to be a LOT of CPU usage. Have you tried adding to that workload with other applications about which you have a general idea of their actual load on your system? I wonder what would happen if you were to load your system to the point that {all other things} are using, say, 77% of your CPU capacity, lol.

Regards,
MDM

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nicotine

Member

Registered: 2015-10-07

Posts: 5

Re: xfce4-taskmanager using lots of cpu

To wrap thing up a bit I have now 3 measurement,
all with a 1 s. delay:

nr. of cores            %CPU (as measured by top)

8                                     2.5
12                                    7.5
24                                   25.0

This does not look good at all. There is is roughly a 3 times increase in CPU time for a 2 time increase in cores.
I will post this on the dev list ToZ  mentioned and if necessary submit bug.

nicotine

Member

Registered: 2015-10-07

Posts: 5

Re: xfce4-taskmanager using lots of cpu

The bug report is here:

https://bugzilla.xfce.org/show_bug.cgi?id=12247