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

[Peter Chen <hzpeterchen@gmail.com>]

On Thu, Nov 03, 2016 at 12:42:11PM +0200, Felipe Balbi wrote:
> 
> Hi,
> 
> Peter Chen <hzpeterchen@gmail.com> writes:
> >> 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?
> 
> what driver are you talking about? Which "local" ethernet driver?
> 

The ethernet driver located at drivers/net/ethernet, its device uses RJ45 connector
to communicate.

-- 

Best Regards,
Peter Chen