On Mon, Jul 27, 2020 at 08:19:43AM -0700, Eric Dumazet wrote:
> On Mon, Jul 27, 2020 at 12:51 AM Jonathan Lemon
> <jonathan.le...@gmail.com> wrote:
> >
> > This flag indicates that the attached data is a zero-copy send,
> > and the pages should be retrieved from the netgpu module. The
> > socket should should already have been attached to a netgpu queue.
> >
> > Signed-off-by: Jonathan Lemon <jonathan.le...@gmail.com>
> > ---
> > include/linux/socket.h | 1 +
> > net/ipv4/tcp.c | 8 ++++++++
> > 2 files changed, 9 insertions(+)
> >
> > diff --git a/include/linux/socket.h b/include/linux/socket.h
> > index 04d2bc97f497..63816cc25dee 100644
> > --- a/include/linux/socket.h
> > +++ b/include/linux/socket.h
> > @@ -310,6 +310,7 @@ struct ucred {
> > */
> >
> > #define MSG_ZEROCOPY 0x4000000 /* Use user data in kernel path */
> > +#define MSG_NETDMA 0x8000000
> > #define MSG_FASTOPEN 0x20000000 /* Send data in TCP SYN */
> > #define MSG_CMSG_CLOEXEC 0x40000000 /* Set close_on_exec for file
> > descriptor received through
> > diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> > index 261c28ccc8f6..340ce319edc9 100644
> > --- a/net/ipv4/tcp.c
> > +++ b/net/ipv4/tcp.c
> > @@ -1214,6 +1214,14 @@ int tcp_sendmsg_locked(struct sock *sk, struct
> > msghdr *msg, size_t size)
> > uarg->zerocopy = 0;
> > }
> >
> > + if (flags & MSG_NETDMA && size && sock_flag(sk, SOCK_ZEROCOPY)) {
> > + zc = sk->sk_route_caps & NETIF_F_SG;
> > + if (!zc) {
> > + err = -EFAULT;
> > + goto out_err;
> > + }
> > + }
> >
>
> Sorry, no, we can not allow adding yet another branch into TCP fast
> path for yet another variant of zero copy.
I'm not in disagreement with that statement, but the existing zerocopy
work makes some assumptions that aren't suitable. I take it that you'd
rather have things folded together so the old/new code works together?
Allocating an extra structure for every skbuff isn't ideal in my book.
> Overall, I think your patch series desperately tries to add changes in
> TCP stack, while there is yet no proof
> that you have to use TCP transport between the peers.
The goal is having a reliable transport without resorting to RDMA.
--
Jonathan
