Re: Debian CPU heating up <no apparent cpu activity>

[Burhan Hanoglu <burhanoglu@gmail.com>]

On Fri, Feb 6, 2015 at 2:59 AM, Bhasker C V <bhasker@unixindia.com> wrote:

could it be because with USB-SSD the kernel detects it as drive (smart
works and also does hdparm) and uses DMA whereas in USB-SD kernel
detects and attaches to usbstor but then has to do pio and cpu
intensive low efficency transfer methods rather than DMA ?
This means that kernel is doing a lot of job to write/read to usb and
will not show up in top ... but still since CPU is being used
constantly CPU gets heated up ....
just a hypothesis ... someone can comment on this

if that is the case how to force UDMA for usb memorystick kind of devices ?
tried googling ... no answer

~$ sudo hdparm -I /dev/sda |grep -E "PIO|DMA"

        DMA: mdma0 mdma1 mdma2 udma0 udma1 udma2 udma3 udma4 *udma5 

        PIO: pio0 pio1 pio2 pio3 pio4 

~$ sudo hdparm -I /dev/sdb |grep -E "PIO|DMA"

SG_IO: bad/missing sense data, sb[]:  70 00 05 00 00 00 00 0a 00 00 00 00 20 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

        DMA: not supported

        PIO: pio0 

That hdparm switch is capital "i", not lowercase "L"...

sda is an ATA drive, and sdb is a usb stick in the above examples. You cannot force that sdb use dma since it doesn't support dma. In case of a drive that supports dma, then "hdparm -d" should help.

I'd expect that even though PIO is a cpu intensive IO, system should not stay that heated when it is idle IO wise. I'd try the same using a usb stick to observe the result and compare...

Regards,

Burhan