From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga06.intel.com ([134.134.136.31]:1701 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751671AbcKCHFc (ORCPT ); Thu, 3 Nov 2016 03:05:32 -0400 From: Felipe Balbi To: Peter Chen , David Miller Cc: linux-usb@vger.kernel.org, ville.syrjala@linux.intel.com, stable@vger.kernel.org Subject: Re: [PATCH] usb: gadget: u_ether: remove interrupt throttling In-Reply-To: <20161103002300.GA894@b29397-desktop> References: <20161101112959.19640-1-felipe.balbi@linux.intel.com> <20161102060202.GD28525@b29397-desktop> <20161102.112254.1243059410485662386.davem@davemloft.net> <20161103002300.GA894@b29397-desktop> Date: Thu, 03 Nov 2016 09:04:54 +0200 Message-ID: <87wpglqc15.fsf@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain Sender: stable-owner@vger.kernel.org List-ID: Hi, Peter Chen writes: > On Wed, Nov 02, 2016 at 11:22:54AM -0400, David Miller wrote: >> From: Peter Chen >> 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