netdev - Re: [PATCH net-next 3/3] net/sched: act

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Date:   Tue, 14 Feb 2023 10:22:20 +0100
From:   Paolo Abeni <pabeni@...hat.com>
To:     Pedro Tammela <pctammela@...atatu.com>, netdev@...r.kernel.org
Cc:     jhs@...atatu.com, xiyou.wangcong@...il.com, jiri@...nulli.us,
        davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org
Subject: Re: [PATCH net-next 3/3] net/sched: act_gate: use percpu stats

On Fri, 2023-02-10 at 17:27 -0300, Pedro Tammela wrote:
> 
> diff --git a/net/sched/act_gate.c b/net/sched/act_gate.c
> index 9b8def0be..684b7a79f 100644
> --- a/net/sched/act_gate.c
> +++ b/net/sched/act_gate.c
> @@ -120,10 +120,10 @@ TC_INDIRECT_SCOPE int tcf_gate_act(struct sk_buff *skb,
>  {
>  	struct tcf_gate *gact = to_gate(a);
>  
> -	spin_lock(&gact->tcf_lock);
> -
>  	tcf_lastuse_update(&gact->tcf_tm);
> -	bstats_update(&gact->tcf_bstats, skb);
> +	tcf_action_update_bstats(&gact->common, skb);
> +
> +	spin_lock(&gact->tcf_lock);

I think that RCU-ifying the 'current_gate_status' field, setting its
value with  WRITE_ONCE (both in _init and in gate_timer_func()) and
finally accessing it here with READ_ONCE, you could move pretty much
everything except the code touching *_octets update outside the
spinlock.

I'm not sure how much that will be relevant - e.g. how frequently we
expect to hit the 

	if (gact->current_max_octets >= 0) {

code path.

For sure the current code allocates per_cpu stats, but they are never
used.

Cheers,

Paolo