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Some odd behaviour ... when sending / uploading files, my CPU usage goes to about 100%; Activity Monitor reports 'Kernel Task' as the culprit. I first noticed this when sending emails in Mail, but it is also happening whenever I use any upload protocol:

  • Email attachment;
  • FTP using Cyberduck or FireFTP (within Firefox);
  • Syncing Evernote (suspect this is also FTP?);
  • FTP via command line (ftp -u)

Any idea why this happens, or how to stop it?

(OSX Lion 10.7.2, Macbook Pro 2.4 Core Duo; customisations include Growl and Quicksilver)

Update: first line of output from top -o cpu:

0      kernel_task  122.3 20:13.81 73/4 0    2     1907

Update 2: Just decided to try this out using wifi instead of my USB 3G modem ... and the problem disappears! Five samples during ftp upload give:

$ top -l 5 -stats pid,command,cpu,th | grep kernel_task
0      kernel_task      0.0  71/2
0      kernel_task      2.2  71/3
0      kernel_task      2.1  71/2
0      kernel_task      2.1  71/2
0      kernel_task      2.2  71/2

So the issue seems to be any upload with the USB modem ... but would still be good to find a solution!

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migrated from Jan 18 '12 at 15:53

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Do you have an antivirus running ? – Shadok Jan 18 '12 at 16:23
@Shadok ... no antivirus! Also tried this after quitting Quicksilver (thinking catalog updates might be happening during uploads), no effect. – Simbamangu Jan 18 '12 at 16:26
Ok, could you try opening a terminal and running 'top' before provoking the problem and pasting the display of the top command when the cpu is bound ? We'll see what's eating the CPU, it should help targeting the problem. – Shadok Jan 18 '12 at 16:40
Hmm... it might related to I/O because I have hard time believing the ftp command would consume such amount of kernel time. Just out of curiosity what is your max bandwith during ftp transfers ? – Shadok Jan 18 '12 at 17:20
Bandwidth goes up to 400 kilobit (USB modem) max, typically half that. Just checked with Mail attachment again (SMTP) and it's the same kernel_task process! – Simbamangu Jan 18 '12 at 17:25

Ok, let's continue here...

It might related to I/O because I have hard time believing the ftp command would consume such amount of kernel time.
A big network transfer rate could be responsible for that though but you should be sending few dozens Mo/s before you hit 100% of CPU on a CPU like this.

Have a look here for a list of things causing kernel_task to go mad and report if you have any luck with it :)

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No luck on that link but see my update 2 above ... – Simbamangu Jan 18 '12 at 17:51

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