Re: [RFC] tcp: Replace TCP buffer structure by an iovec array

[Stefano Brivio <sbrivio@redhat.com>]

On Mon, 11 Mar 2024 14:33:56 +0100
Laurent Vivier <lvivier@redhat.com> wrote:

> To be able to provide pointers to TCP headers and IP headers without
> worrying about alignment in the structure, split the structure into
> several arrays and point to each part of the frame using an iovec array.
> 
> Using iovec also allows us to simply ignore the first entry when the
> vnet length header is not needed. And as the payload buffer contains
> only the TCP header and the TCP data we can increase the size of the
> TCP data to USHRT_MAX - sizeof(struct tcphdr).
> 
> As a side effect, these changes improve performance by a factor of
> x1.5.
> 
> Signed-off-by: Laurent Vivier <lvivier@redhat.com>
> ---
>  tap.c | 104 ++++++++++++++
>  tap.h |  16 +++
>  tcp.c | 429 ++++++++++++++++++++++++----------------------------------
>  3 files changed, 296 insertions(+), 253 deletions(-)
> 
> diff --git a/tap.c b/tap.c
> index c7b9372668ec..afd01cffbed6 100644
> --- a/tap.c
> +++ b/tap.c
> @@ -350,6 +350,30 @@ static size_t tap_send_frames_pasta(const struct ctx *c,
>  	return i;
>  }
>  
> +/**
> + * tap_send_iov_pasta() - Send out multiple prepared frames

...to the pasta tap.

That is, this should get the description of the existing
tap_send_frames_pasta(), and, I guess, tap_send_frames_pasta() should
now switch to writev(), as it's used to send one single message from
multiple buffers, otherwise you'll get a lot of system calls for pasta?

I'm still in the middle of reviewing here, but I thought I would
comment on this right away because it looks quite fundamental.

-- 
Stefano