From owner-freebsd-smp Fri May 31 9:13:45 2002 Delivered-To: freebsd-smp@freebsd.org Received: from evilpete.dyndns.org (12-232-26-46.client.attbi.com [12.232.26.46]) by hub.freebsd.org (Postfix) with ESMTP id 2007737B40B; Fri, 31 May 2002 09:13:07 -0700 (PDT) Received: from overcee.wemm.org ([10.0.0.3]) by evilpete.dyndns.org (8.11.6/8.11.6) with ESMTP id g4VGCu173768; Fri, 31 May 2002 09:13:05 -0700 (PDT) (envelope-from peter@wemm.org) Received: from wemm.org (localhost [127.0.0.1]) by overcee.wemm.org (Postfix) with ESMTP id 5EAFC380A; Fri, 31 May 2002 09:12:56 -0700 (PDT) (envelope-from peter@wemm.org) X-Mailer: exmh version 2.5 07/13/2001 with nmh-1.0.4 To: John Baldwin Cc: Bosko Milekic , freebsd-smp@FreeBSD.ORG, freebsd-hackers@FreeBSD.ORG, Aaro J Koskinen Subject: Re: ICU_LEN with IO APIC In-Reply-To: Date: Fri, 31 May 2002 09:12:56 -0700 From: Peter Wemm Message-Id: <20020531161256.5EAFC380A@overcee.wemm.org> Sender: owner-freebsd-smp@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.org John Baldwin wrote: > > On 31-May-2002 Bosko Milekic wrote: > > > > On Fri, May 31, 2002 at 12:12:00PM +0300, Aaro J Koskinen wrote: > >> Hello, > >> > >> Is there any particular reason why the number of interrupts is limited > >> to 32 on APIC systems? Is it just a conservative guess on the number of > >> interrupts anyone might want to need...? > > > > I'm not sure but perhaps this is historical (and now also required > > again), but if we use a word to mask out interrupts than after 32 we > > run out of bits. "Who needs more than 32 interrupts anyway?!" :-) > > Actually, the historical value in stable is 24 because the same 32-bit word > shares the 8 softinterrupts with 24 hardware interrupts. I think the APIC > only has 32 interrupt pins however. Historically it was because ipending and friends were a 32 bit word. Even now, we have a stack of 32 bit bitfields in this area. It isn't uncommon to have 2 IO apics with 24 pins each. Fortunately there are rarely more than about 20 or so in use in total. Cheers, -Peter -- Peter Wemm - peter@wemm.org; peter@FreeBSD.org; peter@yahoo-inc.com "All of this is for nothing if we don't go to the stars" - JMS/B5 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-smp" in the body of the message