netdev - Re: [net-next PATCH 3/4] net: sched: cls_u32 add bit to specify software only rules

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Date:	Thu, 25 Feb 2016 18:05:45 -0500
From:	Jamal Hadi Salim <jhs@...atatu.com>
To:	John Fastabend <john.fastabend@...il.com>, jiri@...nulli.us,
	daniel@...earbox.net
Cc:	netdev@...r.kernel.org, alexei.starovoitov@...il.com,
	davem@...emloft.net
Subject: Re: [net-next PATCH 3/4] net: sched: cls_u32 add bit to specify
 software only rules

On 16-02-25 04:56 PM, John Fastabend wrote:
> On 16-02-25 04:56 AM, Jamal Hadi Salim wrote:

>
> decoding that is not a problem. The ixgbe driver code already applied
> can decode that without much trouble. The thing I want to avoid is
> requiring my driver to do the inverse translation because although it
> is possible its entirely unnecessary.
>
> To do the above example without a software cache for example
> means I read out row 2048 of a hardware table then you get a bunch of
> bits. From those bits I consult what fields are being loaded into
> the table in the packet processing pipeline. I learn its the src_ip
> fields then I have the value/mask and can unwind it. Finally if I
> collapsed some hash tables onto this hardware table I have to do the
> inverse of my collapsing scheme. The ixgbe one is sort of simple just
> because I only have one table in hardware but with multiple tables
> its a bit more difficult. Finally I've unwound the thing and can
> print something back out of 'tc' but it seems easier to just cache
> the hardware rules somewhere. Maybe other driver/hardware will have
> a different opinion though depending on how much your firmware can
> store and how ambitious you are. Personally I don't see any need
> for the above code.
>

I think if you can cache the rules and have a way to easily map to
the hardware then this would work fine.

cheers,
jamal