Subject: Re: [PATCH net-next 5/9] net/sched: support per action hw stats

From: Simon Horman <[email-masked]>
Date: Fri, 3 Feb 2023 15:33:40 +0100

On Wed, Feb 01, 2023 at 06:10:34PM +0200, Oz Shlomo wrote:
> There are currently two mechanisms for populating hardware stats:
> 1. Using flow_offload api to query the flow's statistics.
>    The api assumes that the same stats values apply to all
>    the flow's actions.
>    This assumption breaks when action drops or jumps over following
>    actions.
> 2. Using hw_action api to query specific action stats via a driver
>    callback method. This api assures the correct action stats for
>    the offloaded action, however, it does not apply to the rest of the
>    actions in the flow's actions array.
> 
> Extend the flow_offload stats callback to indicate that a per action
> stats update is required.
> Use the existing flow_offload_action api to query the action's hw stats.
> In addition, currently the tc action stats utility only updates hw actions.
> Reuse the existing action stats cb infrastructure to query any action
> stats.
> 
> Signed-off-by: Oz Shlomo <[email-masked]>

...

> diff --git a/include/net/pkt_cls.h b/include/net/pkt_cls.h
> index be21764a3b34..d4315757d1a2 100644
> --- a/include/net/pkt_cls.h
> +++ b/include/net/pkt_cls.h
> @@ -292,9 +292,15 @@ static inline void tcf_exts_put_net(struct tcf_exts *exts)
>  #define tcf_act_for_each_action(i, a, actions) \
>  	for (i = 0; i < TCA_ACT_MAX_PRIO && ((a) = actions[i]); i++)
>  
> +static bool tc_act_in_hw(struct tc_action *act)
> +{
> +	return !!act->in_hw_count;
> +}
> +
>  static inline void
>  tcf_exts_hw_stats_update(const struct tcf_exts *exts,
> -			 struct flow_stats *stats)
> +			 struct flow_stats *stats,
> +			 bool use_act_stats)
>  {
>  #ifdef CONFIG_NET_CLS_ACT
>  	int i;
> @@ -302,16 +308,18 @@ static inline void tcf_exts_put_net(struct tcf_exts *exts)
>  	for (i = 0; i < exts->nr_actions; i++) {
>  		struct tc_action *a = exts->actions[i];
>  
> -		/* if stats from hw, just skip */
> -		if (tcf_action_update_hw_stats(a)) {
> -			preempt_disable();
> -			tcf_action_stats_update(a, stats->bytes, stats->pkts, stats->drops,
> -						stats->lastused, true);
> -			preempt_enable();
> -
> -			a->used_hw_stats = stats->used_hw_stats;
> -			a->used_hw_stats_valid = stats->used_hw_stats_valid;
> +		if (use_act_stats || tc_act_in_hw(a)) {
> +			tcf_action_update_hw_stats(a);

Hi Oz,

I am a unclear why it is ok to continue here even if
tcf_action_update_hw_stats() fails.  There seem to be cases other than
!tc_act_in_hw() at play here, which prior to this patch, would execute the
code below that is now outside this if clause.

> +			continue;
>  		}
> +
> +		preempt_disable();
> +		tcf_action_stats_update(a, stats->bytes, stats->pkts, stats->drops,
> +					stats->lastused, true);
> +		preempt_enable();
> +
> +		a->used_hw_stats = stats->used_hw_stats;
> +		a->used_hw_stats_valid = stats->used_hw_stats_valid;
>  	}
>  #endif
>  }
> @@ -769,6 +777,7 @@ struct tc_cls_matchall_offload {
>  	enum tc_matchall_command command;
>  	struct flow_rule *rule;
>  	struct flow_stats stats;
> +	bool use_act_stats;
>  	unsigned long cookie;
>  };
>  
> diff --git a/net/sched/act_api.c b/net/sched/act_api.c
> index 917827199102..eda58b78da13 100644
> --- a/net/sched/act_api.c
> +++ b/net/sched/act_api.c
> @@ -169,11 +169,6 @@ static bool tc_act_skip_sw(u32 flags)
>  	return (flags & TCA_ACT_FLAGS_SKIP_SW) ? true : false;
>  }
>  
> -static bool tc_act_in_hw(struct tc_action *act)
> -{
> -	return !!act->in_hw_count;
> -}
> -
>  /* SKIP_HW and SKIP_SW are mutually exclusive flags. */
>  static bool tc_act_flags_valid(u32 flags)
>  {
> @@ -308,9 +303,6 @@ int tcf_action_update_hw_stats(struct tc_action *action)
>  	struct flow_offload_action fl_act = {};
>  	int err;
>  
> -	if (!tc_act_in_hw(action))
> -		return -EOPNOTSUPP;
> -
>  	err = offload_action_init(&fl_act, action, FLOW_ACT_STATS, NULL);
>  	if (err)
>  		return err;

...