Re: [PATCH] usb: gadget: u_ether: remove interrupt throttling

[Peter Chen <hzpeterchen@gmail.com>]

On Thu, Nov 03, 2016 at 09:04:54AM +0200, Felipe Balbi wrote:
> 
> Hi,
> 
> Peter Chen <hzpeterchen@gmail.com> writes:
> > On Wed, Nov 02, 2016 at 11:22:54AM -0400, David Miller wrote:
> >> From: Peter Chen <hzpeterchen@gmail.com>
> >> Date: Wed, 2 Nov 2016 14:02:02 +0800
> >> 
> >> > Felipe, it may increase cpu utilization since more interrupts will be there,
> >> > it may affect the SoC which has lower cpu frequency. This code existed
> >> > many years, why this problem has only reported at dwc3 recently?
> >> 
> >> It's a bug, and it's going to cause TCP sockets to potentially hang.
> >> 
> >
> > For some controllers, it is, so we need to add parameter for user
> > to see if interrupt migration is supported or not.
> 
> not for some controller, for ALL networking drivers.
> 
> > But just like some ethernet controllers, some USB controllers support
> > hardware timeout mechanism which interrupt will be triggered after
> > some uFrame occurs if the transaction has completed but not required
> > to interrupt, it is used to support interrupt migration like ethernet.
> 
> you're missing the point. What Dave Miller is saying is that it's ALWAYS
> a bug to delay completion of SKBs. The only thing you're doing with
> chipidea is delaying interrupt by up to 125us; which is still a bug from
> the point of view of the networking layer, but it's more difficult to
> perceive any problems because of the short time where interrupt is
> delayed.
> 

If it is ALWAYS a bug to delay completion of SKBs, how the local
ethernet driver designs interrupt migration?

-- 

Best Regards,
Peter Chen