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Subject: Re: [PATCH v1 2/2] virtio-mmio: add features for virtio-mmio
 specification version 3
To:     "Michael S. Tsirkin" <mst@redhat.com>,
        "Liu, Jiang" <gerry@linux.alibaba.com>
Cc:     Jason Wang <jasowang@redhat.com>,
        Zha Bin <zhabin@linux.alibaba.com>,
        linux-kernel@vger.kernel.org, slp@redhat.com,
        virtio-dev@lists.oasis-open.org, jing2.liu@intel.com,
        chao.p.peng@intel.com
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From:   "Liu, Jing2" <jing2.liu@linux.intel.com>
Message-ID: <ec003137-c08f-cda6-6a94-d37d5460189c@linux.intel.com>
Date:   Mon, 6 Jan 2020 15:24:18 +0800
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On 1/5/2020 6:42 PM, Michael S. Tsirkin wrote:
> On Thu, Dec 26, 2019 at 09:16:19PM +0800, Liu, Jiang wrote:
>>> 2) The mask and unmask control is missed
>>>
>>>
>>>>   but the extension doesn’t support 3) because
>>>> we noticed that the Linux virtio subsystem doesn’t really make use of interrupt masking/unmasking.
> Linux uses masking/unmasking in order to migrate interrupts between
> CPUs.

Hi Michael,

Thanks for reviewing the patches!

When trying to study the mask/unmask use case during migrating irq, it 
seems being used e.g.

1) migrate irq(s) away from offline cpu

2) irq affinity is changing, while an interrupt comes so it sets 
SETAFFINITY_PENDING and

the lapic (e.g. x86) does the mask and unmask to finish the pending 
during ack.

Is this right? So we should have mask/unmask for each vector.

Thanks,

Jing