netdev - Re: [PATCH 3/5] vDPA: introduce vDPA bus

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Date:   Tue, 21 Jan 2020 15:57:29 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Shahaf Shuler <shahafs@...lanox.com>,
        "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Jason Gunthorpe <jgg@...lanox.com>,
        Rob Miller <rob.miller@...adcom.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        Netdev <netdev@...r.kernel.org>,
        "Bie, Tiwei" <tiwei.bie@...el.com>,
        "maxime.coquelin@...hat.com" <maxime.coquelin@...hat.com>,
        "Liang, Cunming" <cunming.liang@...el.com>,
        "Wang, Zhihong" <zhihong.wang@...el.com>,
        "Wang, Xiao W" <xiao.w.wang@...el.com>,
        "haotian.wang@...ive.com" <haotian.wang@...ive.com>,
        "Zhu, Lingshan" <lingshan.zhu@...el.com>,
        "eperezma@...hat.com" <eperezma@...hat.com>,
        "lulu@...hat.com" <lulu@...hat.com>,
        Parav Pandit <parav@...lanox.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        "stefanha@...hat.com" <stefanha@...hat.com>,
        "rdunlap@...radead.org" <rdunlap@...radead.org>,
        "hch@...radead.org" <hch@...radead.org>,
        Ariel Adam <aadam@...hat.com>,
        "jakub.kicinski@...ronome.com" <jakub.kicinski@...ronome.com>,
        Jiri Pirko <jiri@...lanox.com>,
        "hanand@...inx.com" <hanand@...inx.com>,
        "mhabets@...arflare.com" <mhabets@...arflare.com>
Subject: Re: [PATCH 3/5] vDPA: introduce vDPA bus


On 2020/1/21 下午2:01, Shahaf Shuler wrote:
> Tuesday, January 21, 2020 12:00 AM, Michael S. Tsirkin:
>> Subject: Re: [PATCH 3/5] vDPA: introduce vDPA bus
>>
>> On Mon, Jan 20, 2020 at 09:47:18PM +0000, Shahaf Shuler wrote:
>>> Monday, January 20, 2020 11:25 PM, Michael S. Tsirkin:
>>>> Subject: Re: [PATCH 3/5] vDPA: introduce vDPA bus
>>>>
>>>> On Mon, Jan 20, 2020 at 08:51:43PM +0000, Shahaf Shuler wrote:
>>>>> Monday, January 20, 2020 7:50 PM, Jason Gunthorpe:
>>>>>> Subject: Re: [PATCH 3/5] vDPA: introduce vDPA bus
>>>>>>
>>>>>> On Mon, Jan 20, 2020 at 04:43:53PM +0800, Jason Wang wrote:
>>>>>>> This is similar to the design of platform IOMMU part of
>>>>>>> vhost-vdpa. We decide to send diffs to platform IOMMU there.
>>>>>>> If it's ok to do that in driver, we can replace set_map with
>>>>>>> incremental API
>>>> like map()/unmap().
>>>>>>> Then driver need to maintain rbtree itself.
>>>>>> I think we really need to see two modes, one where there is a
>>>>>> fixed translation without dynamic vIOMMU driven changes and one
>>>>>> that supports vIOMMU.
>>>>>>
>>>>>> There are different optimization goals in the drivers for these
>>>>>> two configurations.
>>>>> +1.
>>>>> It will be best to have one API for static config (i.e. mapping
>>>>> can be set only before virtio device gets active), and one API for
>>>>> dynamic changes that can be set after the virtio device is active.
>>>> Frankly I don't see when we'd use the static one.
>>>> Memory hotplug is enabled for most guests...
>>> The fact memory hotplug is enabled doesn't necessarily means there is not
>> cold-plugged memory on the hot plugged slots.
>>> So your claim is majority of guests are deployed w/o any cold-plugged
>> memory?
>>
>> Sorry for not being clear. I was merely saying that dynamic one can't be
>> optional, and static one can. So how about we start just with the dynamic
>> one, then add the static one as a later optimization?
> Since we have the use case (cold plugged memory to guest, e.g. when populated w/ hugepages) I think we should start w/ both. The static one can be optional for drivers.
>
> Moreover am not yet clear about the suggested API for dynamic, can you share the prototype you have in mind?
> Also will it be :
> 1. multiple add_map and then flag the driver to set
> Or
> 2. each add_map should be set by the driver as stand alone.


For dynamic one, it looks to me that introducing add_map()/del_map() bus 
operations is much more cleaner than reusing current set_map() one.

Thanks


>