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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id l21sm2638793wmg.41.2021.03.18.08.01.32 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 18 Mar 2021 08:01:33 -0700 (PDT) Subject: Re: [PATCH v2 6/4] selftests: kvm: Add basic Hyper-V clocksources tests To: Vitaly Kuznetsov , kvm@vger.kernel.org Cc: Sean Christopherson , Wanpeng Li , Jim Mattson , Marcelo Tosatti References: <20210316143736.964151-1-vkuznets@redhat.com> <20210318140949.1065740-1-vkuznets@redhat.com> <1176f351-220d-003e-2cae-65f0b42c8f18@redhat.com> <8735ws7bva.fsf@vitty.brq.redhat.com> From: Paolo Bonzini Message-ID: <41897f61-9d1a-519b-e1cb-e19efa34ab55@redhat.com> Date: Thu, 18 Mar 2021 16:01:32 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 MIME-Version: 1.0 In-Reply-To: <8735ws7bva.fsf@vitty.brq.redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 18/03/21 15:52, Vitaly Kuznetsov wrote: > Paolo Bonzini writes: > >> On 18/03/21 15:09, Vitaly Kuznetsov wrote: >>> +static inline void check_tsc_msr_tsc_page(struct ms_hyperv_tsc_page *tsc_page) >>> +{ >>> + u64 r1, r2, t1, t2; >>> + s64 delta_ns; >>> + >>> + /* Compare TSC page clocksource with HV_X64_MSR_TIME_REF_COUNT */ >>> + t1 = mul_u64_u64_shr64(rdtsc(), tsc_page->tsc_scale) + tsc_page->tsc_offset; >>> + r1 = rdmsr(HV_X64_MSR_TIME_REF_COUNT); >>> + nop_loop(); >>> + t2 = mul_u64_u64_shr64(rdtsc(), tsc_page->tsc_scale) + tsc_page->tsc_offset; >>> + r2 = rdmsr(HV_X64_MSR_TIME_REF_COUNT); >>> + >>> + delta_ns = ((r2 - r1) - (t2 - t1)) * 100; >>> + if (delta_ns < 0) >>> + delta_ns = -delta_ns; >>> + >>> + /* 1% tolerance */ >>> + GUEST_ASSERT(delta_ns * 100 < (t2 - t1) * 100); >>> +} >>> + >> >> I think you should also be able to check r1 and r2 individually, not >> just r1 and r2. Is that correct? > > Right, we could've checked r1 == t1 and r2 == t2 actually (with some > tiny margin of course). Let me try that. np, I can do that too. Just checking my recollection of the TLFS. Paolo