Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752691Ab3GXOp7 (ORCPT ); Wed, 24 Jul 2013 10:45:59 -0400 Received: from userp1040.oracle.com ([156.151.31.81]:42649 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751323Ab3GXOp6 (ORCPT ); Wed, 24 Jul 2013 10:45:58 -0400 Date: Wed, 24 Jul 2013 10:45:32 -0400 From: Konrad Rzeszutek Wilk To: Yinghai Lu Cc: Youquan Song , Gleb Natapov , Sheng Yang , Linux Kernel Mailing List , "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , Youquan Song Subject: Re: [PATCH] x86, apic: Enable x2APIC physical when cpu < 256 native Message-ID: <20130724144532.GJ2518@phenom.dumpdata.com> References: <1373592159-459-1-git-send-email-youquan.song@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-Source-IP: ucsinet21.oracle.com [156.151.31.93] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3084 Lines: 62 On Tue, Jul 23, 2013 at 09:24:45PM -0700, Yinghai Lu wrote: > On Thu, Jul 11, 2013 at 6:22 PM, Youquan Song wrote: > > x2APIC extends APICID from 8 bits to 32 bits, but the device interrupt routed > > from IOAPIC or delivered in MSI mode will keep 8 bits destination APICID. > > In order to support x2APIC, the VT-d interrupt remapping is introduced to > > translate the destination APICID to 32 bits in x2APIC mode and keep the device > > compatible in this way. > > > > x2APIC support both logical and physical mode in destination mode. > > In logical destination mode, the 32 bits Logical APICID has 2 sub-fields: > > 16 bits cluster ID and 16 bits logical ID within the cluster and it is > > required VT-d interrupt remapping in x2APIC cluster mode. > > In physical destination mode, the 8 bits physical id is compatible with 32 > > bits physical id when CPU number < 256. > > When interrupt remapping initialization fail on platform with CPU number < 256, > > current kernel only enables x2APIC physical mode in virutalization environment, ^^^^^^^^^^^^^^-virtualization > > while we also can enable x2APIC physcial mode in native kernel this situation, ^^^^^^^ physical > > and the device interrupt will use 8 bits destination APICID in physical mode > > and be compatible with x2APIC physical when < 256 CPUs. > > > > So we can benefit from x2APIC vs xAPIC MMIO: > > - x2APIC MSR read/write is faster than xAPIC mmio > > - x2APIC only ICR write to deliver interrupt without polling ICR deliver > > status bit and xAPIC need poll to read ICR deliver status bit. > > - x2APIC 64 bits ICR access instead of xAPIC two 32 bits access. > > > > Signed-off-by: Youquan Song > > --- > > arch/x86/kernel/apic/apic.c | 7 ++----- > > 1 files changed, 2 insertions(+), 5 deletions(-) > > > > diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c > > index 904611b..51a065a 100644 > > --- a/arch/x86/kernel/apic/apic.c > > +++ b/arch/x86/kernel/apic/apic.c > > @@ -1603,11 +1603,8 @@ void __init enable_IR_x2apic(void) > > goto skip_x2apic; > > > > if (ret < 0) { > > - /* IR is required if there is APIC ID > 255 even when running > > - * under KVM > > - */ > > - if (max_physical_apicid > 255 || > > - !hypervisor_x2apic_available()) { > > + /* IR is required if there is APIC ID > 255 */ > > + if (max_physical_apicid > 255) { > > if (x2apic_preenabled) > > disable_x2apic(); > > goto skip_x2apic; > > Those are kvm and xen related. > > Add more Cc. > > Yinghai -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/