Re: High CPU load produced by USB (DW2)

[gregkh <gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org>]

On Wed, Feb 07, 2018 at 10:48:57AM +0100, Mirza Krak wrote:
> Hi.
> 
> I initially started a thread on a different mailing list [1], and you
> can take look there for some additional background.
> 
> I am using a 4.14.15 stable kernel on a RK3288 SoC (FireFly RK3288
> board) which uses the DW2 USB core. I have noticed that when
> connecting a USB device there is unreasonable high CPU load produced
> by the USB interrupts.

That's a normal problem with that kind of hardware.  I've seen devices
with that type of USB core take a 30% cpu usage just when you plug a USB
keyboard into the device.

There's not much the kernel can do about horrible hardware, sorry, go
complain to the device manufacturer :(

> Here is one example with a MIDI keyboard connected on USB (not really
> doing anything on it)
> 
>    79     2 root     SW       0   0%  19% [irq/45-dwc2_hso]
>    78     2 root     SW       0   0%  11% [irq/45-ff540000]

It doesn't matter if anything is happening on the device, USB goes and
polls the device all the time, that's just the way that the protocol
works.  With hardware like this, that polling is done by the kernel
driver/CPU and does not have offload capability to the USB controller to
handle this type of housekeeping.  Because of that, you see tons of CPU
interrupts and a high load.

Again, not much we can do about that, sorry :(

good luck!

greg k-h
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