From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Sun, 19 Jan 2003 20:18:34 +0000 From: Arjan van de Ven Subject: Re: 2.5.59-mm2 Message-ID: <20030119201834.A3965@devserv.devel.redhat.com> References: <3014AAAC8E0930438FD38EBF6DCEB5647D1492@fmsmsx407.fm.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3014AAAC8E0930438FD38EBF6DCEB5647D1492@fmsmsx407.fm.intel.com>; from jun.nakajima@intel.com on Sun, Jan 19, 2003 at 11:45:35AM -0800 Sender: owner-linux-mm@kvack.org Return-Path: To: "Nakajima, Jun" Cc: arjanv@redhat.com, Andrew Morton , linux-mm@kvack.org, "Kamble, Nitin A" , "Mallick, Asit K" , "Saxena, Sunil" List-ID: On Sun, Jan 19, 2003 at 11:45:35AM -0800, Nakajima, Jun wrote: > We initially implemented it in user level, accessing /proc/interrupts. We have two issues/concerns at that point. And we saw better results with kernel mode. > - the data structures required, such as kstat, are already in the kernel > and converting the text info from /proc/interrupts was costly in > user mode. costly is a relative thing. a dozen cycles perhaps; do it once per 10 seconds and it's invisbile. I agree that if you want to do it thousands of times per second it might become a problem.But so far I don't see the real need for that. > - we suspect that frequent writes (asynchronous to interrupts) > to /proc/irq/N/smp_affinity might expose a race condition in interrupt > machinery. For example, we saw a hang caused by such a write. if there's a bug there it needs fixing anyway; even inside the kernel you'll have a similar race I suspect > So to implement it in user level efficiently, we need API that > - that provide binary data that can be easily processed by such a daemon, there is rightfully a veto on such ABI and it's also not needed. /proc/interrupts is less than 4Kb normally; it'll be in cache so parsing it will be cheap. Sure the code I posted isn't optimal (far from it) but that can be optimized a lot. Greetings, Arjan van de Ven -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/