Fwd: [RFC PATCH net-next 0/3] virtio_net: add aRFS support

[Zhi Yong Wu <zwu.kernel@gmail.com>]

CC: stefanha, MST, Rusty Russel

---------- Forwarded message ----------
From: Jason Wang <jasowang@redhat.com>
Date: Thu, Jan 16, 2014 at 12:23 PM
Subject: Re: [RFC PATCH net-next 0/3] virtio_net: add aRFS support
To: Zhi Yong Wu <zwu.kernel@gmail.com>
Cc: netdev@vger.kernel.org, therbert@google.com, edumazet@google.com,
davem@davemloft.net, Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>


On 01/15/2014 10:20 PM, Zhi Yong Wu wrote:
>
> From: Zhi Yong Wu<wuzhy@linux.vnet.ibm.com>
>
> HI, folks
>
> The patchset is trying to integrate aRFS support to virtio_net. In this case,
> aRFS will be used to select the RX queue. To make sure that it's going ahead
> in the correct direction, although it is still one RFC and isn't tested, it's
> post out ASAP. Any comment are appreciated, thanks.
>
> If anyone is interested in playing with it, you can get this patchset from my
> dev git on github:
>    git://github.com/wuzhy/kernel.git virtnet_rfs
>
> Zhi Yong Wu (3):
>    virtio_pci: Introduce one new config api vp_get_vq_irq()
>    virtio_net: Introduce one dummy function virtnet_filter_rfs()
>    virtio-net: Add accelerated RFS support
>
>   drivers/net/virtio_net.c      |   67 ++++++++++++++++++++++++++++++++++++++++-
>   drivers/virtio/virtio_pci.c   |   11 +++++++
>   include/linux/virtio_config.h |   12 +++++++
>   3 files changed, 89 insertions(+), 1 deletions(-)
>

Please run get_maintainter.pl before sending the patch. You'd better
at least cc virtio maintainer/list for this.

The core aRFS method is a noop in this RFC which make this series no
much sense to discuss. You should at least mention the big picture
here in the cover letter. I suggest you should post a RFC which can
run and has expected result or you can just raise a thread for the
design discussion.

And this method has been discussed before, you can search "[net-next
RFC PATCH 5/5] virtio-net: flow director support" in netdev archive
for a very old prototype implemented by me. It can work and looks like
most of this RFC have already done there.

A basic question is whether or not we need this, not all the mq cards
use aRFS (see ixgbe ATR). And whether or not it can bring extra
overheads? For virtio, we want to reduce the vmexits as much as
possible but this aRFS seems introduce a lot of more of this. Making a
complex interfaces just for an virtual device may not be good, simple
method may works for most of the cases.

We really should consider to offload this to real nic. VMDq and L2
forwarding offload may help in this case.


-- 
Regards,

Zhi Yong Wu