debug a high load average

debug a high load average

[Rajesh]

Hi All:

I have a case occasionally when I copy data from a usb storage (ipod) to 
my hard drive the load average goes up from 0.4 to about 15.0, and the 
system becomes very unusable till I kill the cp command. I have checked 
the CPU usage, bytes read from usb device, byte written to hard drive 
etc, and all these values are low like CPU usage is at a maximum of 30%, 
disk read bytes is at an average of 1.5 MiB/s, disk write bytes is at 
1.5 MiB/s, number of processes is at 110, etc, during this high load.

So my question is what else determines the high load average that in 
turn is resulting in the unresponsiveness of the system? What else 
should I be looking for to debug the problem?

Thanks a lot,
Rajesh

Re: debug a high load average

[Erik Mouw]

On Tue, Aug 23, 2005 at 04:38:36PM +0530, Rajesh wrote:
> I have a case occasionally when I copy data from a usb storage (ipod) to 
> my hard drive the load average goes up from 0.4 to about 15.0, and the 
> system becomes very unusable till I kill the cp command. I have checked 
> the CPU usage, bytes read from usb device, byte written to hard drive 
> etc, and all these values are low like CPU usage is at a maximum of 30%, 
> disk read bytes is at an average of 1.5 MiB/s, disk write bytes is at 
> 1.5 MiB/s, number of processes is at 110, etc, during this high load.

1.5 MB/s suggests you're using an IDE drive in PIO mode. Switch to DMA
mode (hdparm -d 1 /dev/hda) and see if it gets any better.


Erik

-- 
+-- Erik Mouw -- www.harddisk-recovery.com -- +31 70 370 12 90 --
| Lab address: Delftechpark 26, 2628 XH, Delft, The Netherlands

Re: debug a high load average

[Rajesh]

Erik Mouw wrote:

>On Tue, Aug 23, 2005 at 04:38:36PM +0530, Rajesh wrote:
>  
>
>>I have a case occasionally when I copy data from a usb storage (ipod) to 
>>my hard drive the load average goes up from 0.4 to about 15.0, and the 
>>system becomes very unusable till I kill the cp command. I have checked 
>>the CPU usage, bytes read from usb device, byte written to hard drive 
>>etc, and all these values are low like CPU usage is at a maximum of 30%, 
>>disk read bytes is at an average of 1.5 MiB/s, disk write bytes is at 
>>1.5 MiB/s, number of processes is at 110, etc, during this high load.
>>    
>>
>
>1.5 MB/s suggests you're using an IDE drive in PIO mode. Switch to DMA
>mode (hdparm -d 1 /dev/hda) and see if it gets any better.
>
>  
>

It seems to have helped a little. Now the rate at which load average 
goes up has decreased ( I can copy up to about 700-800 MiB compared to a 
high of 200MiB earlier), but it is still going up to 15 gradually at 
which point I am still killing the cp process to make the system usable.

I know I am not giving much information. But if I know what factors 
cause the loadavg to keep on going up I will gladly provide it.

I am running  2.6.12 kernel on a laptop. I have an ipod attached to my 
USB 1.1 as a drive on which I am saving and retreiving large 
files(2-4GiB files). The transfer speed is slow, but I am fine with it, 
as long as the load average stays within bounds so that the machine is 
usable. (If I dual boot to windows and do the same operation, I am able 
to get the files copied over in a few minutes.). Can vfat be a factor?

Thanks
Rajesh

>Erik
>
>  
>

Re: debug a high load average

[Mariusz Zielinski]

On Wednesday 24 August 2005 06:40, you wrote:
[...]
> I am running  2.6.12 kernel on a laptop. I have an ipod attached to my
> USB 1.1 as a drive on which I am saving and retreiving large
> files(2-4GiB files). 
[...]

Check if you are not using low performance usb driver (CONFIG_BLK_DEV_UB).
If I remember correctly it uses /dev/ub* devices.

-- 
Mariusz Zielinski