linux-kernel - Re: [RFC] Question about enable doorbell irq and halt

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Message-ID: <f04863f2-1b50-3c66-e4cb-0cd8da239c77@huawei.com>
Date:   Wed, 20 Mar 2019 22:31:36 +0800
From:   Heyi Guo <guoheyi@...wei.com>
To:     "Tangnianyao (ICT)" <tangnianyao@...wei.com>,
        <kvm@...r.kernel.org>, <kvmarm@...ts.cs.columbia.edu>,
        <linux-kernel@...r.kernel.org>, Linuxarm <linuxarm@...wei.com>
CC:     <wanghaibin.wang@...wei.com>, Marc Zyngier <marc.zyngier@....com>,
        Christoffer Dall <christoffer.dall@....com>
Subject: Re: [RFC] Question about enable doorbell irq and halt_poll process

+cc Marc and Christoffer...


On 2019/3/19 21:25, Tangnianyao (ICT) wrote:
> Hi, all
>
> Using gicv4, when guest is waiting for irq, it sends wfi and traps to kvm.
> When vlpi is forwarded to PE after its_vpe_deschedule, before halt_poll in
> kvm_vcpu_block, halt_poll may increase latency for this vlpi getting to guest.
> In halt_poll process, it checks if there's pending irq for vcpu using pending_last.
> However, doorbell is not enable at this moment and vlpi or doorbell can not set
> pending_last true, to stop halt_poll. It will run until halt_poll time ends, if
> there's no other physical irq coming in the meantime. And then vcpu is scheduled out.
> This pending vlpi has to wait for vcpu getting schedule in next time.
>
> Should we enable doorbell before halt_poll process ?
>
>
> .
>