From: Sean Christopherson <seanjc@google.com>
To: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: kvm@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
Maxim Levitsky <mlevitsk@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] KVM: selftests: Make hyperv_clock selftest more stable
Date: Wed, 1 Jun 2022 16:06:43 +0000 [thread overview]
Message-ID: <YpeOkx0gkINeKFuz@google.com> (raw)
In-Reply-To: <20220601144322.1968742-1-vkuznets@redhat.com>
On Wed, Jun 01, 2022, Vitaly Kuznetsov wrote:
> hyperv_clock doesn't always give a stable test result, especially with
> AMD CPUs. The test compares Hyper-V MSR clocksource (acquired either
> with rdmsr() from within the guest or KVM_GET_MSRS from the host)
> against rdtsc(). To increase the accuracy, increase the measured delay
> (done with nop loop) by two orders of magnitude and take the mean rdtsc()
> value before and after rdmsr()/KVM_GET_MSRS.
Rather than "fixing" the test by reducing the impact of noise, can we first try
to reduce the noise itself? E.g. pin the test to a single CPU, redo the measurement
if the test is interrupted (/proc/interrupts?), etc... Bonus points if that can
be implemented as a helper or pair of helpers so that other tests that want to
measure latency/time don't need to reinvent the wheel.
next prev parent reply other threads:[~2022-06-01 16:06 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-01 14:43 [PATCH] KVM: selftests: Make hyperv_clock selftest more stable Vitaly Kuznetsov
2022-06-01 16:06 ` Sean Christopherson [this message]
2022-06-02 13:34 ` Vitaly Kuznetsov
2022-06-07 8:07 ` Maxim Levitsky
2022-06-07 8:26 ` Maxim Levitsky
2022-06-07 15:22 ` Paolo Bonzini
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