linux-kernel - Re: [PATCH v4 5/5] KVM: LAPIC: Narrow the timer latency between wait_lapic

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Message-ID: <YKQR9rq9WNT6dauh@google.com>
Date:   Tue, 18 May 2021 19:13:58 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Wanpeng Li <kernellwp@...il.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH v4 5/5] KVM: LAPIC: Narrow the timer latency between
 wait_lapic_expire and world switch

On Tue, May 18, 2021, Wanpeng Li wrote:
> From: Wanpeng Li <wanpengli@...cent.com>
> 
> Let's treat lapic_timer_advance_ns automatic tuning logic as hypervisor
> overhead, move it before wait_lapic_expire instead of between wait_lapic_expire 
> and the world switch, the wait duration should be calculated by the 
> up-to-date guest_tsc after the overhead of automatic tuning logic. This 
> patch reduces ~30+ cycles for kvm-unit-tests/tscdeadline-latency when testing 
> busy waits.
> 
> Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
> ---

Reviewed-by: Sean Christopherson <seanjc@...gle.com>