Re: [PATCH RFC 0/4] vsock/virtio: optimizations to increase the throughput

[Jason Wang]

On 2019/4/8 äå5:44, Stefan Hajnoczi wrote:
> On Mon, Apr 08, 2019 at 02:43:28PM +0800, Jason Wang wrote:
> > Another thing that may help is to implement sendpage(), which will greatly
> > improve the performance.
> I can't find documentation for ->sendpage().  Is the idea that you get a
> struct page for the payload and can do zero-copy tx?


Yes.


>   (And can userspace
> still write to the page, invalidating checksums in the header?)
>
> Stefan


Userspace can still write to the page, but for correctness (e.g in the 
case of SPLICE_F_GIFT describe by vmsplice(2)), it should not do this. 
For vmsplice, it may hard to detect the time to reuse the page. Maybe we 
MSG_ZEROCOPY[1] is better.

Anyway, sendpage() could be still useful for sendfile() or splice().

Thanks

[1] https://netdevconf.org/2.1/papers/netdev.pdf