From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [RFC PATCH v3 2/2] add support for Hyper-V partition reference time enlightenment Date: Tue, 10 Dec 2013 17:52:22 +0100 Message-ID: <52A746C6.2020608@redhat.com> References: <1386502419-26614-1-git-send-email-vrozenfe@redhat.com> <1386502419-26614-3-git-send-email-vrozenfe@redhat.com> <52A5D497.1070308@redhat.com> <1386674597.32091.55.camel@localhost> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org, mtosatti@redhat.com, pl@dlhnet.de To: Vadim Rozenfeld Return-path: Received: from mail-qc0-f171.google.com ([209.85.216.171]:40092 "EHLO mail-qc0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751929Ab3LJQwb (ORCPT ); Tue, 10 Dec 2013 11:52:31 -0500 Received: by mail-qc0-f171.google.com with SMTP id c9so4095442qcz.16 for ; Tue, 10 Dec 2013 08:52:30 -0800 (PST) In-Reply-To: <1386674597.32091.55.camel@localhost> Sender: kvm-owner@vger.kernel.org List-ID: Il 10/12/2013 12:23, Vadim Rozenfeld ha scritto: > > > + if (kvm->arch.hv_tsc_page & HV_X64_MSR_TSC_REFERENCE_ENABLE) { > > > + HV_REFERENCE_TSC_PAGE* tsc_ref; > > > + u64 curr_time; > > > + tsc_ref = (HV_REFERENCE_TSC_PAGE*)gfn_to_hva(kvm, > > > + kvm->arch.hv_tsc_page >> HV_X64_MSR_TSC_REFERENCE_ADDRESS_SHIFT); > > > + tsc_ref->tsc_sequence = > > > + boot_cpu_has(X86_FEATURE_CONSTANT_TSC) ? tsc_ref->tsc_sequence + 1 : 0; > > > + tsc_ref->tsc_scale = ((10000LL << 32) / __get_cpu_var(cpu_tsc_khz)) << 32; > > > > Why shouldn't this be vcpu->arch.virtual_tsc_khz? > > Yeah, I was thinking about that, but we need a vcpu instance for this. You can perhaps store the value from vcpu->arch.virtual_tsc_khz to kvm->arch when the MSR is first written? > Do you mean between HV_X64_MSR_REFERENCE_TSC which happens during > partition creation time and KVM_SET_CLOCK which happens during resume > after partition pause? If so - there are several differences, where > the offset calculation probably is the most important one. The offset and frequence are the only differences. + curr_time = (((tsc_ref->tsc_scale >> 32) * native_read_tsc()) >> 32) + + tsc_ref->tsc_offset; + tsc_ref->tsc_offset = kvm->arch.hv_ref_time - curr_time; Why do you need kvm->arch.hv_ref_time at all? Can you just use "get_kernel_ns() + kvm->arch.kvmclock_offset - kvm->arch.hv_ref_count"? Then the same code can set tsc_ref->tsc_offset in both cases. In fact, it's not clear to me what hv_ref_time is for, and how it is different from By the way, a small nit: > > + tsc_ref.tsc_sequence = > + boot_cpu_has(X86_FEATURE_CONSTANT_TSC) ? 1 : 0; > + tsc_ref.tsc_scale = > + ((10000LL << 32) / vcpu->arch.virtual_tsc_khz) << 32; > + tsc_ref.tsc_offset = 0; > if (__copy_to_user((void __user *)addr, &tsc_ref, sizeof(tsc_ref))) > return 1; > mark_page_dirty(kvm, gfn); > kvm->arch.hv_tsc_page = data; > + kvm->arch.hv_ref_count = 0; > break; This setting of kvm->arch.hv_ref_count belongs in the previous patch. Paolo