#12538 NORM 4-softw: XO-4 CPU usage at idle is high

[Zarro Boogs per Child]

#12538: XO-4 CPU usage at idle is high
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           Reporter:  dsd           |       Owner:  cjb          
               Type:  defect        |      Status:  new          
           Priority:  normal        |   Milestone:  4-software   
          Component:  not assigned  |     Version:  not specified
         Resolution:                |    Keywords:               
        Next_action:  never set     |    Verified:  0            
Deployment_affected:                |   Blockedby:               
           Blocking:                |  
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Comment(by dsd):

 I tested some different vanilla kernel versions, comparing against our
 OLPC kernel. Booting without X, running "top" and watching the idle % for
 about a minute.

 {{{
 olpc 3.5: 85%, varying +/- 5%
 olpc 3.5 nohz=off: 96% constant

 3.5: 99%, frequently fluctuating all the way down to 0% for no apparent
 reason
 3.5 nohz=off: 99% constant

 3.5.7 behaves the same as 3.5

 3.6: 98%, frequently fluctuating all the way down to 0% for no apparent
 reason
 3.6 nohz=off:  99% constant

 3.7: 96% , varying +/- 3%
 3.7 nohz=off: 98% constant
 }}}

 Conclusions:
  * All the kernels behave badly with nohz enabled, up until 3.7. Will
 explore the possibility of disabling nohz for now on XO-4 - main
 consideration is impact on power usage.
  * Something in the OLPC 3.5 kernel causes behaviour to differ from the
 vanilla 3.5 kernel. Or it could be a difference in .config. It would be
 nice to know what this is.

-- 
Ticket URL: <http://dev.laptop.org/ticket/12538#comment:5>
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