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

On 3/8/24 09:34, Stefano Brivio wrote:
...
  On Fri, 8 Mar 2024 09:18:48 +0100
 Laurent Vivier <lvivier(a)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) 
ok...

...
  ...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.
  
I hope to have something to test today...

Thanks,
Laurent