From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759922AbYGKBvR (ORCPT ); Thu, 10 Jul 2008 21:51:17 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754777AbYGKBvB (ORCPT ); Thu, 10 Jul 2008 21:51:01 -0400 Received: from mga11.intel.com ([192.55.52.93]:50460 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754307AbYGKBvA (ORCPT ); Thu, 10 Jul 2008 21:51:00 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.30,341,1212390000"; d="scan'208";a="353247470" Date: Thu, 10 Jul 2008 18:50:59 -0700 From: Suresh Siddha To: Yong Wang Cc: "Eric W. Biederman" , "Siddha, Suresh B" , "mingo@elte.hu" , "hpa@zytor.com" , "tglx@linutronix.de" , "akpm@linux-foundation.org" , "arjan@linux.intel.com" , "andi@firstfloor.org" , "jbarnes@virtuousgeek.org" , "steiner@sgi.com" , "linux-kernel@vger.kernel.org" Subject: Re: [patch 26/26] x64, x2apic/intr-remap: introduce CONFIG_INTR_REMAP Message-ID: <20080711015059.GO1678@linux-os.sc.intel.com> References: <20080710181634.764954000@linux-os.sc.intel.com> <20080710182239.635284000@linux-os.sc.intel.com> <20080710233733.GA21085@ywang-dev> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20080710233733.GA21085@ywang-dev> User-Agent: Mutt/1.4.1i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 10, 2008 at 04:37:33PM -0700, Yong Wang wrote: > > Is it possible to run in x2apic mode without running in interrupt remapping mode? > > Just send the irqs directly to the cpu? It feels like it should be if an iommu > > doesn't get in the way. > > > > Yes, it is possible to run in x2apic mode without intr-remap. However, the extended > cpu addressability will not be fully utilized that way. No. CPU can't be in x2apic mode with out enabling interrupt-remapping. Interrupts may not work (even when we have few cpu's). For example, in logical cluster mode, logical x2apic id (initialized by HW) will be > 16 bit, in a smaller DP configuration. In general, enabling x2apic with out enabling interrupt-remapping is not recommended, as the platform will be using legacy interrupt format and the CPU will be using extended ID mode. thanks, suresh