From mboxrd@z Thu Jan 1 00:00:00 1970 From: Suresh Siddha Subject: Re: [PATCH v5] enable x2APIC without interrupt remapping under KVM Date: Wed, 01 Jul 2009 14:00:17 -0700 Message-ID: <1246482017.27006.10670.camel@localhost.localdomain> References: <20090701133007.GC27539@redhat.com> Reply-To: suresh.b.siddha@intel.com Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Cc: "linux-kernel@vger.kernel.org" , Sheng Yang , "kvm@vger.kernel.org" , "avi@redhat.com" , mingo@elte.hu To: Gleb Natapov Return-path: Received: from mga11.intel.com ([192.55.52.93]:44288 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750914AbZGAVDW (ORCPT ); Wed, 1 Jul 2009 17:03:22 -0400 In-Reply-To: <20090701133007.GC27539@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On Wed, 2009-07-01 at 06:30 -0700, Gleb Natapov wrote: > KVM would like to provide x2APIC interface to a guest without emulating > interrupt remapping device. The reason KVM prefers guest to use x2APIC > is that x2APIC interface is better virtualizable and provides better > performance than mmio xAPIC interface: > > - msr exits are faster than mmio (no page table walk, emulation) > - no need to read back ICR to look at the busy bit > - one 64 bit ICR write instead of two 32 bit writes > - shared code with the Hyper-V paravirt interface > > Included patch changes x2APIC enabling logic to enable it even if IR > initialization failed, but kernel runs under KVM and no apic id is > greater than 255 (if there is one spec requires BIOS to move to x2apic > mode before starting an OS). > > Signed-off-by: Gleb Natapov Acked-by: Suresh Siddha