[CentOS] High load averages with latest kernel and USB drives?

Todd Denniston Todd.Denniston at tsb.cranrdte.navy.mil
Fri Nov 20 12:43:02 UTC 2009

Benjamin Smith wrote, On 11/18/2009 06:11 PM:
> On Tuesday 17 November 2009 15:37:24 Todd Denniston wrote:
>> Benjamin Smith wrote, On 11/17/2009 01:46 PM:
>>> See comments below...
>>> On Tuesday 17 November 2009 07:52:01 Todd Denniston wrote:
>>>> Benjamin Smith wrote, On 11/16/2009 10:56 PM:
>>>>> I have a 1TB USB drive plugged into a USB2 port that I use to back up
>>>>> the production drives (which are SCSI). It's working fine, but while
>>>>> doing backups (hourly) the load average on the server shoots up from
>>>>> the normal 0.5 - 1.5 or so up to a high between 10 and 30. Strangely,
>>>>> even though the "load is high" the server is completely responsive,
>>>>> even the USB drives being accessed are!
>>>>> Using top to diagnose, nothing seems to be particularly high! IoWait
>>>>> seems reasonable (10-30%) and CPUs are 0.5%, Idle is 70-90%. Even
>>>>> accessing the USB partition while the load is "high" is responsive!
>> you might add another field to top while you are watching, Last used cpu
>>  (SMP), i.e., start top
>> press f
>> press j
>> press enter
>> this should let you see if your process is bouncing between processors.
> The process pg_dump is "adhering" fine to processor 1. I see usb-storage 
> bouncing between processors - I've seen it on 3, 4, 7 over perhaps a minute. 
> What could you recommend next? 

#2 set the usb-storage on a particular set of processors,
# Note USBSTORPID= line prototyped on CentOS 5 machine not 4.
USBSTORPID=`ps aux |grep usb-storage|head -1 |awk '{print $2}'`
taskset -p -c 4 $USBSTORPID

and still
I have not had the taskset of the USB driver cause faults when used on a dual processor Xeon, but if 
any of the above breaks your system you get to keep the chunky bits. :0

so if you try it, keep an eye on it.
reversing the above taskset in your case would I _think_ be:
taskset -p -c 0-7 $USBSTORPID

Todd Denniston
Crane Division, Naval Surface Warfare Center (NSWC Crane)
Harnessing the Power of Technology for the Warfighter

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