netdev - Re: [PATCH net-next 10/13] net/sched: add block pointer to tc_cls_common

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Date:   Sun, 5 May 2019 13:34:32 -0400
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Jiri Pirko <jiri@...nulli.us>
Cc:     davem@...emloft.net, netdev@...r.kernel.org,
        oss-drivers@...ronome.com, xiyou.wangcong@...il.com,
        idosch@...lanox.com, f.fainelli@...il.com, andrew@...n.ch,
        vivien.didelot@...il.com, gerlitz.or@...il.com,
        simon.horman@...ronome.com,
        Pieter Jansen van Vuuren 
        <pieter.jansenvanvuuren@...ronome.com>
Subject: Re: [PATCH net-next 10/13] net/sched: add block pointer to
 tc_cls_common_offload structure

On Sat, 4 May 2019 15:16:54 +0200, Jiri Pirko wrote:
> Sat, May 04, 2019 at 01:46:25PM CEST, jakub.kicinski@...ronome.com wrote:
> >From: Pieter Jansen van Vuuren <pieter.jansenvanvuuren@...ronome.com>
> >
> >Some actions like the police action are stateful and could share state
> >between devices. This is incompatible with offloading to multiple devices
> >and drivers might want to test for shared blocks when offloading.
> >Store a pointer to the tcf_block structure in the tc_cls_common_offload
> >structure to allow drivers to determine when offloads apply to a shared
> >block.  
> 
> I don't this this is good idea. If your driver supports shared blocks,
> you should register the callback accordingly. See:
> mlxsw_sp_setup_tc_block_flower_bind() where tcf_block_cb_lookup() and
> __tcf_block_cb_register() are used to achieve that.

Right, in some ways.  Unfortunately we don't support shared blocks
fully, i.e. we register multiple callbacks and get the rules
replicated.  It's a FW limitation, but I don't think we have shared
blocks on the roadmap, since rule storage is not an issue for our HW.

But even if we did support sharing blocks, we'd have to teach TC that
some rules can only be offloaded if there is only a single callback
registered, right?  In case the block is shared between different ASICs.