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

[Felipe Balbi <felipe.balbi@linux.intel.com>]

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.

-- 
balbi