From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261858AbVFLALK (ORCPT ); Sat, 11 Jun 2005 20:11:10 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261859AbVFLALK (ORCPT ); Sat, 11 Jun 2005 20:11:10 -0400 Received: from gateway-1237.mvista.com ([12.44.186.158]:41711 "EHLO av.mvista.com") by vger.kernel.org with ESMTP id S261858AbVFLALH (ORCPT ); Sat, 11 Jun 2005 20:11:07 -0400 Subject: Re: [PATCH] local_irq_disable removal From: Sven-Thorsten Dietrich To: tglx@linutronix.de Cc: Daniel Walker , Ingo Molnar , Esben Nielsen , linux-kernel@vger.kernel.org In-Reply-To: <1118533485.13312.91.camel@tglx.tec.linutronix.de> References: <1118533485.13312.91.camel@tglx.tec.linutronix.de> Content-Type: text/plain Date: Sat, 11 Jun 2005 17:09:52 -0700 Message-Id: <1118534993.5593.175.camel@sdietrich-xp.vilm.net> Mime-Version: 1.0 X-Mailer: Evolution 2.0.4 (2.0.4-4) Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 2005-06-12 at 01:44 +0200, Thomas Gleixner wrote: > On Sat, 2005-06-11 at 13:51 -0700, Daniel Walker wrote: > > On Sat, 11 Jun 2005, Ingo Molnar wrote: > > > Interesting .. So "cli" takes 7 cycles , "sti" takes 7 cycles. The current > > method does "lea" which takes 1 cycle, and "or" which takes 1 cycle. I'm > > not sure if there is any function call overhead .. So the soft replacment > > of cli/sti is 70% faster on a per instruction level .. So it's at least > > not any slower .. Does everyone agree on that? > > No, because x86 is not the whole universe > Das Dehnt sich aus. Even if there is a case of minimal expansion in the overhead on some architecture, it may justify the effort for a certain class of applications which require known interrupt response latencies. The concept model here is, that you will have all interrupts running in threads, EXCEPT one or more SA_NODELAY real-time IRQs. Those RT-IRQs may be required to track satellites, manage I/O for a QOS or RF protocol stack, shut down a SAW, or a variety of RT-related services. The IRQ-disable-removal allows that the RT-IRQ encounters minimal delay. Often, that IRQ will also wake up a process, and that process may have some response-time constraints on it, as well. SO that's one model that is helped by this design.