netdev - Re: [net-next PATCH 0/5] net_sched: Add support for IFE action

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Message-ID: <56CDECE5.5040604@iogearbox.net>
Date:	Wed, 24 Feb 2016 18:48:21 +0100
From:	Daniel Borkmann <daniel@...earbox.net>
To:	Jamal Hadi Salim <jhs@...atatu.com>, davem@...emloft.net
CC:	netdev@...r.kernel.org, xiyou.wangcong@...il.com,
	alexei.starovoitov@...il.com
Subject: Re: [net-next PATCH 0/5] net_sched: Add support for IFE action

On 02/24/2016 01:49 PM, Jamal Hadi Salim wrote:
> On 16-02-23 10:34 AM, Daniel Borkmann wrote:
>> On 02/23/2016 03:28 PM, Jamal Hadi Salim wrote:
> [..]
>
>>> These are basic metadata. The question to ask is what could one use
>>> skb->hash for. Today it is used to select a cpu to balance to.
>>
>> Right, but that happens before you decode that information from your TLV
>> on ingress qdisc. And any subsequent skb_get_hash() to read out skb->hash
>> will effectively overwrite what you set there and call into flow dissector.
>
> Drivers do set the hash. My use case is slightly different.
> I have a NIC which has an embedded cavium processor. This thing
> strips off the TLV and uses the hash to select the host MSI.
> Only thing we dont use at the moment is queue_mapping.

Ok, but the example says ingress qdisc. ;) I presume the driver for the
NIC and the offloading parts are non-public? :/ So, without them, placing
this on ingress qdisc doesn't seem much useful wrt the skb hash example,
and most people only have the software part (for ingress I mean) available.