Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [virtio-dev] Re: [PATCH v1 2/2] virtio-mmio: add features for
 virtio-mmio specification version 3
To:     "Liu, Jing2" <jing2.liu@linux.intel.com>,
        Zha Bin <zhabin@linux.alibaba.com>,
        linux-kernel@vger.kernel.org
Cc:     mst@redhat.com, slp@redhat.com, virtio-dev@lists.oasis-open.org,
        gerry@linux.alibaba.com, jing2.liu@intel.com, chao.p.peng@intel.com
References: <cover.1577240905.git.zhabin@linux.alibaba.com>
 <a11d4c616158c9fb1ca4575ca0530b2e17b952fa.1577240905.git.zhabin@linux.alibaba.com>
 <85eeab19-1f53-6c45-95a2-44c1cfd39184@redhat.com>
 <28da67db-73ab-f772-fb00-5a471b746fc5@linux.intel.com>
 <683cac51-853d-c8c8-24c6-b01886978ca4@redhat.com>
 <42346d41-b758-967a-30b7-95aa0d383beb@linux.intel.com>
From:   Jason Wang <jasowang@redhat.com>
Message-ID: <0c3d33de-3940-7895-2fe2-81de8714139c@redhat.com>
Date:   Fri, 3 Jan 2020 11:24:48 +0800
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101
 Thunderbird/60.8.0
MIME-Version: 1.0
In-Reply-To: <42346d41-b758-967a-30b7-95aa0d383beb@linux.intel.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: quoted-printable
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


On 2020/1/2 =E4=B8=8B=E5=8D=885:13, Liu, Jing2 wrote:
> [...]
>
>>>>
>>>>> +
>>>>> +/* RO: MSI feature enabled mask */
>>>>> +#define VIRTIO_MMIO_MSI_ENABLE_MASK=C2=A0=C2=A0=C2=A0 0x8000
>>>>> +/* RO: Maximum queue size available */
>>>>> +#define VIRTIO_MMIO_MSI_STATUS_QMASK=C2=A0=C2=A0=C2=A0 0x07ff
>>>>> +/* Reserved */
>>>>> +#define VIRTIO_MMIO_MSI_STATUS_RESERVED=C2=A0=C2=A0=C2=A0 0x7800
>>>>> +
>>>>> +#define VIRTIO_MMIO_MSI_CMD_UPDATE=C2=A0=C2=A0=C2=A0 0x1
>>>>
>>>>
>>>> I believe we need a command to read the number of vectors supported=20
>>>> by the device, or 2048 is assumed to be a fixed size here?
>>>
>>> For not bringing much complexity, we proposed vector per queue and=20
>>> fixed relationship between events and vectors.
>>
>>
>> It's a about the number of MSIs not the mapping between queues to=20
>> MSIs.And it looks to me it won't bring obvious complexity, just need=20
>> a register to read the #MSIs. Device implementation may stick to a=20
>> fixed size.
>
> Based on that assumption, the device supports #MSIs =3D #queues +=20
> #config. Then driver need not read the register.
>
> We're trying to make such kind of agreement on spec level.


Ok, I get you now.

But still, having fixed number of MSIs is less flexible. E.g:

- for x86, processor can only deal with about 250 interrupt vectors.
- driver may choose to share MSI vectors [1] (which is not merged but we=20
will for sure need it)

[1] https://lkml.org/lkml/2014/12/25/169


>
>>
>> Having few pages for a device that only have one queue is kind of a=20
>> waste.
>
> Could I ask what's the meaning of few pages here? BTW, we didn't=20
> define MSIx-like tables for virtio-mmio.


I thought you're using a fixed size (2048) for each device. But looks not=
 :)

Thanks


>
> Thanks,
>
> Jing
>
>>
>> Thanks
>>
>>
>>>
>>>
>>> So the number of vectors supported by device is equal to the total=20
>>> number of vqs and config.
>>>
>>> We will try to explicitly highlight this point in spec for later=20
>>> version.
>>>
>>>
>>> Thanks!
>>>
>>> Jing
>>>
>>>>
>>>> --------------------------------------------------------------------=
-
>>>> To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org
>>>> For additional commands, e-mail: virtio-dev-help@lists.oasis-open.or=
g
>>>>
>>>
>>
>
> ---------------------------------------------------------------------
> To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org
> For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org
>