Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1163021AbbKFUkL (ORCPT ); Fri, 6 Nov 2015 15:40:11 -0500 Received: from mail-wi0-f178.google.com ([209.85.212.178]:34123 "EHLO mail-wi0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1161947AbbKFUkI (ORCPT ); Fri, 6 Nov 2015 15:40:08 -0500 Subject: Re: [PATCH v2 00/12] KVM: x86: add support for VMX TSC scaling To: kvm@vger.kernel.org, Gleb Natapov , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , x86@kernel.org, Joerg Roedel , Wanpeng Li , Xiao Guangrong , mdontu@bitdefender.com, Kai Huang , Andy Lutomirski , linux-kernel@vger.kernel.org References: <1445326752-8926-1-git-send-email-haozhong.zhang@intel.com> <563C85A4.1080006@redhat.com> <20151106124251.GA15818@hzzhang-OptiPlex-9020.sh.intel.com> From: Paolo Bonzini Message-ID: <563D1022.9050100@redhat.com> Date: Fri, 6 Nov 2015 21:40:02 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 MIME-Version: 1.0 In-Reply-To: <20151106124251.GA15818@hzzhang-OptiPlex-9020.sh.intel.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2806 Lines: 68 On 06/11/2015 13:42, Haozhong Zhang wrote: > On 11/06/15 11:49, Paolo Bonzini wrote: >> >> >> On 20/10/2015 09:39, Haozhong Zhang wrote: >>> This patchset adds support for VMX TSC scaling feature which is >>> available on Intel Skylake CPU. The specification of VMX TSC scaling >>> can be found at >>> http://www.intel.com/content/www/us/en/processors/timestamp-counter-scaling-virtualization-white-paper.html >>> >>> VMX TSC scaling allows guest TSC which is read by guest rdtsc(p) >>> instructions increases in a rate that is customized by the hypervisor >>> and can be different than the host TSC rate. Basically, VMX TSC >>> scaling adds a 64-bit field called TSC multiplier in VMCS so that, if >>> VMX TSC scaling is enabled, TSC read by guest rdtsc(p) instructions >>> will be calculated by the following formula: >>> >>> guest EDX:EAX = (Host TSC * TSC multiplier) >> 48 + VMX TSC Offset >>> >>> where, Host TSC = Host MSR_IA32_TSC + Host MSR_IA32_TSC_ADJUST. >>> >>> This patchset, when cooperating with another QEMU patchset (sent in >>> another email "target-i386: save/restore vcpu's TSC rate during >>> migration"), allows guest programs observe a consistent TSC rate even >>> though they are migrated among machines with different host TSC rates. >>> >>> VMX TSC scaling shares some common logics with SVM TSC ratio which >>> is already supported by KVM. Patch 1 ~ 8 move those common logics from >>> SVM code to the common code. Upon them, patch 9 ~ 12 add VMX-specific >>> support for VMX TSC scaling. >>> >>> Changes in v2: >>> * Remove the duplicated variable 'kvm_tsc_scaling_ratio_rsvd'. >>> * Remove an unnecessary error check in original patch 2. >>> * Do 64-bit arithmetic by functions recommended by Paolo. >>> * Make kvm_set_tsc_khz() returns an error number so that ioctl >>> KVM_SET_TSC_KHZ does not return 0 if errors happen. >>> >>> Reviewed-by: Eric Northup >> >> Thanks for the patches. There are a couple changes that I can do myself: >> >> 1) kvm_default_tsc_scaling_ratio can be initialized in >> kvm_arch_hardware_setup, since it's just 1ULL << >> kvm_tsc_scaling_ratio_frac_bits >> > Agree > >> 2) things that you are adding to include/linux/kvm_host.h should instead >> go in arch/x86/include/linux/kvm_host.h >> > Agree, because they are x86 specific. > >> That's it. I'll commit it as soon as I test on AMD (today hopefully). It tested fine. I'll give it a shot with the 32-bit mul_u64_u64_shr on Monday as well, but I don't expect any issue. Thanks, the patches are neat! Paolo -- 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/