From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ming Zhang Subject: Re: hwo to adjust interrupt? Date: Fri, 12 Aug 2005 13:45:26 -0400 Message-ID: <1123868726.5546.89.camel@localhost.localdomain> References: Reply-To: mingz@ele.uri.edu Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Return-path: Received: from leviathan.ele.uri.edu ([131.128.51.64]:20172 "EHLO leviathan.ele.uri.edu") by vger.kernel.org with ESMTP id S1750757AbVHLRpk (ORCPT ); Fri, 12 Aug 2005 13:45:40 -0400 In-Reply-To: Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: Bryan Henderson Cc: Arjan van de Ven , linux-scsi On Fri, 2005-08-12 at 10:35 -0700, Bryan Henderson wrote: > >>How much extra work does Linux have to do for each interrupt? > > > >usually 1 pci mmio read; the rest is negligible. > > I was hoping you would cater better to my ignorance of how PCI interrupt > handling works in Linux. > > Is it the case that Linux invokes the registered interrupt handler of each > of the drivers for the devices that share the interrupt, and each does an > mmio read of its device to find out if it had reason to generate an > interrupt? So the waste is that extra call, and you're saying the CPU > instructions involved are negligible compared to the mmio read? > > Are these level-sensitive interrupts, so that if both devices need service > at the same time, they generate just one interrupt and neither device > driver call is wasted? > i guess so. also sound like the intr overhead is not that big as i assumed. so if i really want to make myself comfortable, i can disable the share interrupt when register interrupt in driver code, rite? ming