Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754098AbbKXOcH (ORCPT ); Tue, 24 Nov 2015 09:32:07 -0500 Received: from mx1.redhat.com ([209.132.183.28]:37434 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753397AbbKXOcE (ORCPT ); Tue, 24 Nov 2015 09:32:04 -0500 Date: Tue, 24 Nov 2015 15:31:55 +0100 From: Radim =?utf-8?B?S3LEjW3DocWZ?= To: "Wu, Feng" Cc: "pbonzini@redhat.com" , "kvm@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] KVM: x86: Add lowest-priority support for vt-d posted-interrupts Message-ID: <20151124143154.GB13925@potion.brq.redhat.com> References: <1447037208-75615-1-git-send-email-feng.wu@intel.com> <20151116190314.GA12245@potion.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1674 Lines: 33 2015-11-24 01:26+0000, Wu, Feng: > "I don't think we do any vector hashing on our client parts. This may be why the customer is not able to detect this on Skylake client silicon. > The vector hashing is micro-architectural and something we had done on server parts. > > If you look at the haswell server CPU spec (https://www-ssl.intel.com/content/dam/www/public/us/en/documents/datasheets/xeon-e5-v3-datasheet-vol-2.pdf) > In section 4.1.2, you will see an IntControl register (this is a register controlled/configured by BIOS) - see below. Thank you! > If you look at bits 6:4 in that register, you see the option we offer in hardware for what kind of redirection is applied to lowest priority interrupts. > There are three options: > 1. Fixed priority > 2. Redirect last > 3. Hash Vector > > If picking vector hash, then bits 10:8 specifies the APIC-ID bits used for the hashing." The hash function just interprets a subset of vector's bits as a number and uses that as a starting offset in a search for an enabled APIC within the destination set? For example: The x2APIC destination is 0x00000055 (= first four even APICs in cluster 0), the vector is 0b11100000, and bits 10:8 of IntControl are 000. 000 means that bits 7:4 of vector are selected, thus the vector hash is 0b1110 = 14, so the round-robin effectively does 14 % 4 (because we only have 4 destinations) and delivers to the 3rd possible APIC (= ID 6)? -- 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/