From mboxrd@z Thu Jan 1 00:00:00 1970 From: Radim =?utf-8?B?S3LEjW3DocWZ?= Subject: Re: [PATCH v2] KVM: hyperv: support HV_X64_MSR_TSC_FREQUENCY and HV_X64_MSR_APIC_FREQUENCY Date: Wed, 26 Jul 2017 14:49:54 +0200 Message-ID: <20170726124954.GA2551@flask> References: <20170726113259.11395-1-lprosek@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Cc: kvm@vger.kernel.org, pbonzini@redhat.com To: Ladi Prosek Return-path: Received: from mx1.redhat.com ([209.132.183.28]:53118 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751441AbdGZMt5 (ORCPT ); Wed, 26 Jul 2017 08:49:57 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 44AC87F41F for ; Wed, 26 Jul 2017 12:49:57 +0000 (UTC) Content-Disposition: inline In-Reply-To: <20170726113259.11395-1-lprosek@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: 2017-07-26 13:32+0200, Ladi Prosek: > It has been experimentally confirmed that supporting these two MSRs is one > of the necessary conditions for nested Hyper-V to use the TSC page. Modern > Windows guests are noticeably slower when they fall back to reading > timestamps from the HV_X64_MSR_TIME_REF_COUNT MSR instead of using the TSC > page. > > The newly supported MSRs are advertised with the AccessFrequencyRegs > partition privilege flag and CPUID.40000003H:EDX[8] "Support for > determining timer frequencies is available" (both outside of the scope of > this KVM patch). > Signed-off-by: Ladi Prosek > --- > > v1->v2: > * HV_X64_MSR_TSC_FREQUENCY now based on vcpu->arch.virtual_tsc_khz (Radim) > * Removed both MSRs from the partition-wide list as the implementation is > no longer vcpu agnostic I like that we don't have to add a capability to expose this feature to the userspace, Reviewed-by: Radim Krčmář