netdev - Re: [PATCH net-next 2/2] net: sched: Lockless Token Bucket (LTB) Qdisc

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Message-Id: <20200706.132947.1139798465163322137.davem@davemloft.net>
Date:   Mon, 06 Jul 2020 13:29:47 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     xiangning.yu@...baba-inc.com
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH net-next 2/2] net: sched: Lockless Token Bucket (LTB)
 Qdisc

From: "YU, Xiangning" <xiangning.yu@...baba-inc.com>
Date: Tue, 07 Jul 2020 02:08:13 +0800

> Lockless Token Bucket (LTB) is a qdisc implementation that controls the
> use of outbound bandwidth on a shared link. With the help of lockless
> qdisc, and by decoupling rate limiting and bandwidth sharing, LTB is
> designed to scale in the cloud data centers.
> 
> Signed-off-by: Xiangning Yu <xiangning.yu@...baba-inc.com>

I'm very skeptical about having a kthread for each qdisc, that doesn't
sound like a good idea at all.

Also:

> +static inline struct ltb_skb_cb *ltb_skb_cb(const struct sk_buff *skb)

No inline functions in foo.c files please.

> +static inline s64 get_linkspeed(struct net_device *dev)

Likewise.

> +static inline int ltb_drain(struct ltb_class *cl)
> +{
> +	typeof(&cl->drain_queue) queue;

Use the actual type not typeof().

> +	struct sk_buff *skb;
> +	int npkts, bytes;
> +	unsigned long now = NOW();
> +	int cpu;
> +	struct ltb_sched *ltb = qdisc_priv(cl->root_qdisc);
> +	struct ltb_pcpu_sched *pcpu_q;
> +	s64 timestamp;
> +	bool need_watchdog = false;
> +	struct cpumask cpumask;

Please order local variables in reverse christmas tree order.

> +static void ltb_aggregate(struct ltb_class *cl)
> +{
> +	s64 timestamp = ktime_get_ns();
> +	struct ltb_sched *ltb = qdisc_priv(cl->root_qdisc);
> +	int num_cpus = ltb->num_cpus;
> +	int i;

Likewise.

> +static inline void ltb_fanout(struct ltb_sched *ltb)
> +{

No inline please.

> +/* How many classes within the same group want more bandwidth */
> +static inline int bw_class_want_more_count(struct list_head *head)
> +{
> +	int n = 0;
> +	struct ltb_class *cl;

No inline, and reverse christmas tree ordering for local variables.

> +/* Redistribute bandwidth among classes with the same priority */
> +static int bw_redistribute_prio(struct list_head *lhead, int bw_available,
> +				int n, bool *all_reached_ceil)
> +{
> +	struct ltb_class *cl;
> +	int avg = 0;
> +	int orig_bw_allocated;
> +	int safe_loop = 0;
> +

Likewise.

> +static int bw_redistribute(struct ltb_sched *ltb, int bw_available)
> +{
> +	int prio = 0;
> +	int n;
> +	int highest_non_saturated_prio = TC_LTB_NUMPRIO;
> +	bool all_reached_ceil;

Likewise.

> +static void bw_balance(struct ltb_sched *ltb)
> +{
> +	struct ltb_class *cl;
> +	s64 link_speed = ltb->link_speed;
> +	int bw_available = link_speed;
> +	s64 total = 0;
> +	int high = TC_LTB_NUMPRIO;
> +	int is_light_traffic = 1;
> +	int i;

Likewise.

And so on and so forth.  This code needs a lot of style fixes
and removal of the per-qdisc kthread design.

Thank you.