netdev - Re: [ RFC net-next 2/3] net: flow_offload: add action stats api

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Date:   Tue, 16 Aug 2022 14:42:04 +0100
From:   Edward Cree <ecree.xilinx@...il.com>
To:     Oz Shlomo <ozsh@...dia.com>, netdev@...r.kernel.org
Cc:     Jiri Pirko <jiri@...dia.com>, Jamal Hadi Salim <jhs@...atatu.com>,
        Simon Horman <simon.horman@...igine.com>,
        Baowen Zheng <baowen.zheng@...igine.com>,
        Vlad Buslov <vladbu@...dia.com>,
        Ido Schimmel <idosch@...dia.com>, Roi Dayan <roid@...dia.com>
Subject: Re: [ RFC net-next 2/3] net: flow_offload: add action stats api

On 16/08/2022 10:23, Oz Shlomo wrote:
> The current offload api provides visibility to flow hw stats.
> This works as long as the flow stats values apply to all the flow's
> actions. However, this assumption breaks when an action, such as police,
> decides to drop or jump over other actions.
> 
> Extend the flow_offload api to return stat record per action instance.
> Use the per action stats value, if available, when updating the action
> instance counters.
> 
> Signed-off-by: Oz Shlomo <ozsh@...dia.com>

When I worked on this before I tried with a similar "array of action
 stats" API [1], but after some discussion it seemed cleaner to have
 a "get stats for one single action" callback [2] which then could
 be called in a loop for filter dumps but also called singly for
 action dumps (RTM_GETACTION).  I recommend this approach to your
 consideration.

[1]: https://lore.kernel.org/all/9804a392-c9fd-8d03-7900-e01848044fea@solarflare.com/
[2]: https://lore.kernel.org/all/a3f0a79a-7e2c-4cdc-8c97-dfebe959ab1f@solarflare.com/

> diff --git a/net/sched/cls_flower.c b/net/sched/cls_flower.c
> index 7da3337c4356..7dc8a62796b5 100644
> --- a/net/sched/cls_flower.c
> +++ b/net/sched/cls_flower.c
> @@ -499,7 +499,9 @@ static void fl_hw_update_stats(struct tcf_proto *tp, struct cls_fl_filter *f,
>  	tc_setup_cb_call(block, TC_SETUP_CLSFLOWER, &cls_flower, false,
>  			 rtnl_held);
>  
> -	tcf_exts_hw_stats_update(&f->exts, &cls_flower.stats);
> +	tcf_exts_hw_stats_update(&f->exts, &cls_flower.stats, cls_flower.act_stats);
> +
> +	kfree(cls_flower.act_stats);
>  }

Perhaps I'm being dumb, but I don't see this being allocated
 anywhere.  Is the driver supposed to be responsible for doing so?
 That seems inelegant.

-ed