netdev - Re: [RFC PATCH net-next 3/3] virtio-net: Add accelerated RFS support

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Message-ID: <CA+mtBx8eRuWpYkYoPbuCaO1h0Y+g96zJB96zP17ZixOwZ1_gmQ@mail.gmail.com>
Date:	Fri, 17 Jan 2014 20:59:15 -0800
From:	Tom Herbert <therbert@...gle.com>
To:	Ben Hutchings <bhutchings@...arflare.com>
Cc:	Zhi Yong Wu <zwu.kernel@...il.com>,
	Stefan Hajnoczi <stefanha@...hat.com>,
	Linux Netdev List <netdev@...r.kernel.org>,
	Eric Dumazet <edumazet@...gle.com>,
	"David S. Miller" <davem@...emloft.net>,
	Zhi Yong Wu <wuzhy@...ux.vnet.ibm.com>
Subject: Re: [RFC PATCH net-next 3/3] virtio-net: Add accelerated RFS support

Ben,

I've never quite understood why flow management in aRFS has to be done
with separate messages, and if I recall this seems to mitigate
performance gains to a large extent. It seems like we should be able
to piggyback on a TX descriptor for a connection information about the
RX side for that connection, namely the rxhash and queue mapping.
State creation should be implicit by just seeing a new rxhash value,
tear down might be accomplished with a separate flag on the final TX
packet on the connection (this would need some additional logic in the
stack). Is this method not feasible in either NICs or virtio-net?

On Fri, Jan 17, 2014 at 9:20 AM, Ben Hutchings
<bhutchings@...arflare.com> wrote:
> On Sat, 2014-01-18 at 00:54 +0800, Zhi Yong Wu wrote:
>> On Fri, Jan 17, 2014 at 7:16 AM, Ben Hutchings
>> <bhutchings@...arflare.com> wrote:
> [...]
>> > However, to take advantage of ARFS on a physical net driver, it would be
>> > necessary to send a control request for part 2.
>> aRFS on a physical net driver? What is this physical net driver? I
>> thought that in order to enable aRFS, guest virtio_net driver should
>> send a control request to its emulated virtio_net NIC.
> [...]
>
> If the backend is connected to a macvlan device on top of a physical net
> device that supports ARFS, then there is further potential for improving
> performance by steering to the best physical RX queue and CPU as well as
> the best virtio_net RX queue and vCPU.
>
> Ben.
>
> --
> Ben Hutchings, Staff Engineer, Solarflare
> Not speaking for my employer; that's the marketing department's job.
> They asked us to note that Solarflare product names are trademarked.
>
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