Re: [PATCH 0/4] Some improvements to the tap send path

[Stefano Brivio <sbrivio@redhat.com>]

On Fri, 8 Mar 2024 09:18:48 +0100
Laurent Vivier <lvivier@redhat.com> wrote:

> On 3/8/24 07:53, David Gibson wrote:
> > This series has a handful of small improvements to the tap send path.
> > See individual commit messages for the details.
> > 
> > I expect this will conflict with Laurent's upcoming work.  I hope the
> > conflicts won't be too bad, and indeed will set us up for less
> > duplication there in the end.  
> 
> I'm working on patch that devides TCP buffers in several buffers pointed out by an IOV 
> arrays and then provided to tap_send_frames(). I'm going to base my patch on this series.
> 
> The idea is:
> 
> A frame is made with 4 iovecs:
> 
> #define TCP_IOV_VNET    0
> #define TCP_IOV_ETH     1
> #define TCP_IOV_IP      2
> #define TCP_IOV_PAYLOAD 3
> #define TCP_IOV_NUM     4
> typedef struct iovec tap_iovec_t[TCP_IOV_NUM];

Except for the typedef :) (I'm actively trying to discourage them)
...this looks very neat.

I would suggest that as soon as you have something barely spitting out
pseudo-correct bytes, you give it a try with perf(1). I'm quite
concerned that we might end up killing throughput, especially without
vhost-user, even though in theory it all sounds nice and byte-saving.

-- 
Stefano