From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S270899AbUKAPV7 (ORCPT ); Mon, 1 Nov 2004 10:21:59 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S263093AbUKAOM0 (ORCPT ); Mon, 1 Nov 2004 09:12:26 -0500 Received: from h-68-165-86-241.dllatx37.covad.net ([68.165.86.241]:10023 "EHLO sol.microgate.com") by vger.kernel.org with ESMTP id S262764AbUKAOLB (ORCPT ); Mon, 1 Nov 2004 09:11:01 -0500 Message-ID: <418643E2.9080006@microgate.com> Date: Mon, 01 Nov 2004 08:10:42 -0600 From: Paul Fulghum User-Agent: Mozilla Thunderbird 0.8 (Windows/20040913) X-Accept-Language: en-us, en MIME-Version: 1.0 To: Stuart MacDonald CC: "'Alan Cox'" , "'Russell King'" , "'Linux Kernel Mailing List'" Subject: Re: [BUG][2.6.8.1] serial driver hangs SMP kernel, but not the UPkernel References: <000201c4bfe2$7389eeb0$294b82ce@stuartm> In-Reply-To: <000201c4bfe2$7389eeb0$294b82ce@stuartm> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Stuart MacDonald wrote: > From: Paul Fulghum > I always thought the whole point of low_latency was to make the > receive-path very fast, which means specifically allowing the flip > routine to run from the ISR. So checking for calling from the ISR and > specifically disallowing that is basically negating the entire raison > d'etre for low_latency. I was thought it was to speed processing if the caller was already in process context. Maybe the real intentions are lost to history. Moving forward, Alan stated that the flip routine should not be called in interrupt context. His last post concerning some transient state of low_latency has confused me. Currently, with the 8250 driver and N_TTY line discipline, calling the flip routine from ISR causes an SMP deadlock. There are two paths that cause this: 1. low_latency is set 2. flip buffer becomes full So calling the flip routine from the ISR may work with some specific drivers, but it would be dangerous to assume this works in all cases. -- Paul Fulghum paulkf@microgate.com