From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ming Zhang Subject: Re: hwo to adjust interrupt? Date: Fri, 12 Aug 2005 15:05:51 -0400 Message-ID: <1123873551.5546.116.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]:6530 "EHLO leviathan.ele.uri.edu") by vger.kernel.org with ESMTP id S1751244AbVHLTGB (ORCPT ); Fri, 12 Aug 2005 15:06:01 -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 i tried to remove the SA_SHIRQ option when request_irq(), unfortunately it seems that the IO-APIC will only try to allocate same # to it and once that slot is used, the request_irq will fail. ming 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? >