Re: [PATCH net-next 0/3] vhost: accelerate metadata access through vmap()

[David Miller]

From: Jason Wang <jasowang@xxxxxxxxxx>
Date: Fri, 14 Dec 2018 12:29:54 +0800

> 
> On 2018/12/14 上午4:12, Michael S. Tsirkin wrote:
>> On Thu, Dec 13, 2018 at 06:10:19PM +0800, Jason Wang wrote:
>>> Hi:
>>>
>>> This series tries to access virtqueue metadata through kernel virtual
>>> address instead of copy_user() friends since they had too much
>>> overheads like checks, spec barriers or even hardware feature
>>> toggling.
>>>
>>> Test shows about 24% improvement on TX PPS. It should benefit other
>>> cases as well.
>>>
>>> Please review
>> I think the idea of speeding up userspace access is a good one.
>> However I think that moving all checks to start is way too aggressive.
> 
> 
> So did packet and AF_XDP. Anyway, sharing address space and access
> them directly is the fastest way. Performance is the major
> consideration for people to choose backend. Compare to userspace
> implementation, vhost does not have security advantages at any
> level. If vhost is still slow, people will start to develop backends
> based on e.g AF_XDP.

Exactly, this is precisely how this kind of problem should be solved.

Michael, I strongly support the approach Jason is taking here, and I
would like to ask you to seriously reconsider your objections.

Thank you.