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Subject: Re: [PATCH] KVM: Boost vCPU candidiate in user mode which is
 delivering interrupt
To:     Sean Christopherson <seanjc@google.com>,
        Wanpeng Li <kernellwp@gmail.com>
Cc:     LKML <linux-kernel@vger.kernel.org>, kvm <kvm@vger.kernel.org>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>
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From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <c1909fa3-61f3-de6b-1aa1-8bc36285e1e4@redhat.com>
Date:   Mon, 19 Apr 2021 18:59:13 +0200
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On 19/04/21 18:32, Sean Christopherson wrote:
> If false positives are a big concern, what about adding another pass to the loop
> and only yielding to usermode vCPUs with interrupts in the second full pass?
> I.e. give vCPUs that are already in kernel mode priority, and only yield to
> handle an interrupt if there are no vCPUs in kernel mode.
> 
> kvm_arch_dy_runnable() pulls in pv_unhalted, which seems like a good thing.

pv_unhalted won't help if you're waiting for a kernel spinlock though, 
would it?  Doing two passes (or looking for a "best" candidate that 
prefers kernel mode vCPUs to user mode vCPUs waiting for an interrupt) 
seems like the best choice overall.

Paolo