Re: [PATCH v1 0/2] Virtio-net PMD Extension to work on host

["Tan, Jianfeng" <jianfeng.tan@intel.com>]

On 1/6/2016 11:57 AM, Tetsuya Mukawa wrote:
> On 2015/12/28 20:06, Tetsuya Mukawa wrote:
>> On 2015/12/24 23:05, Tan, Jianfeng wrote:
>>> Hi Tetsuya,
>>>
>>> After several days' studying your patch, I have some questions as follows:
>>>
>>> 1. Is physically-contig memory really necessary?
>>> This is a too strong requirement IMHO. IVSHMEM doesn't require this in its original meaning. So how do you think of
>>> Huawei Xie's idea of using virtual address for address translation? (In addition, virtual address of mem_table could be
>>> different in application and QTest, but this can be addressed because SET_MEM_TABLE msg will be intercepted by
>>> QTest)
>> Hi Jianfeng,
>>
>> Thanks for your suggestion.
>> Huawei's idea may solve contig-mem restriction.
>> Let me have time to check it more.
> Hi Jianfeng,
>
> I made sure we can remove the restriction with Huawei's idea.
> One thing I concern is below.
> If we don't use contiguous memory, this PMD will not work with other
> 'physical' PMDs like e1000 PMD, virtio-net PMD, and etc.
> (This is because allocated memory may not  be physically contiguous.)
>
> One of examples is that if we implement like above, in QEMU guest, we
> can handle a host NIC directly, but in container, we will not be able to
> handle the device.
> This will be a restriction for this virtual addressing changing.
>
> Do you know an use case that the user wants to handle 'physical' PMD and
> 'virtual' virtio-net PMD together?
>
> Tetsuya,
Hi Tetsuya,

I have no use case in hand, which handles 'physical' PMDs and 'virtual' 
virtio-net PMD together.
(Pavel Fedin once tried to run ovs in container, but that case just uses 
virtual virtio devices, I
don't know if he has plan to add 'physical' PMDs as well.)

Actually, it's not completely contradictory to make them work together. 
Like this:
a. containers with root privilege
We can initialize memory as legacy way. (TODO: besides 
physical-contiguous, we try allocate
virtual-contiguous big area for all memsegs as well.)
a.1 For vhost-net, before sending memory regions into kernel, we can 
merge those virtual-contiguous regions into one region.
a.2 For vhost-user, we can merge memory regions in the vhost. The 
blocker is that for now, maximum fd num was restricted
by VHOST_MEMORY_MAX_NREGIONS=8 (so in 2M-hugepage's case, 16M shared 
memory is not nearly enough).

b. containers without root privilege
No need to worry about this problem, because it lacks of privilege to 
construct physical-contiguous memory.

Thanks,
Jianfeng