linux-kernel - Re: [PATCH net-next 1/3] net: Introduce netif_xmit_time_out

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Message-ID: <20251127173437.479d27fa@kernel.org>
Date: Thu, 27 Nov 2025 17:34:37 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Tariq Toukan <tariqt@...dia.com>
Cc: Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
 Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller"
 <davem@...emloft.net>, Jian Shen <shenjian15@...wei.com>, Salil Mehta
 <salil.mehta@...wei.com>, Jijie Shao <shaojijie@...wei.com>, Saeed Mahameed
 <saeedm@...dia.com>, Mark Bloch <mbloch@...dia.com>, Leon Romanovsky
 <leon@...nel.org>, Jamal Hadi Salim <jhs@...atatu.com>, Cong Wang
 <xiyou.wangcong@...il.com>, Jiri Pirko <jiri@...nulli.us>,
 <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
 <linux-rdma@...r.kernel.org>, Gal Pressman <gal@...dia.com>, Moshe Shemesh
 <moshe@...dia.com>, Yael Chemla <ychemla@...dia.com>, Shahar Shitrit
 <shshitrit@...dia.com>
Subject: Re: [PATCH net-next 1/3] net: Introduce
 netif_xmit_time_out_duration() helper

On Tue, 25 Nov 2025 09:12:54 +0200 Tariq Toukan wrote:
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index e808071dbb7d..3cd73769fcfa 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h

include/net/net_queue.h seems like a better place for new code

> @@ -3680,6 +3680,21 @@ static inline bool netif_xmit_stopped(const struct netdev_queue *dev_queue)
>  	return dev_queue->state & QUEUE_STATE_ANY_XOFF;
>  }
>  
> +static inline unsigned int
> +netif_xmit_timeout_ms(struct netdev_queue *txq, unsigned long *trans_start)
> +{
> +	unsigned long txq_trans_start = READ_ONCE(txq->trans_start);
> +
> +	if (trans_start)
> +		*trans_start = txq_trans_start;

The drivers don't really care about this, AFAICT hns3 uses this
to calculate the stall length (return value of this func.

> +	if (netif_xmit_stopped(txq) &&
> +	    time_after(jiffies, txq_trans_start + txq->dev->watchdog_timeo))
> +		return jiffies_to_msecs(jiffies - txq_trans_start);
> +
> +	return 0;
> +}
> +
>  static inline bool
>  netif_xmit_frozen_or_stopped(const struct netdev_queue *dev_queue)
>  {
> diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
> index 852e603c1755..aa6192781a24 100644
> --- a/net/sched/sch_generic.c
> +++ b/net/sched/sch_generic.c
> @@ -523,10 +523,9 @@ static void dev_watchdog(struct timer_list *t)
>  				 * netdev_tx_sent_queue() and netif_tx_stop_queue().
>  				 */
>  				smp_mb();
> -				trans_start = READ_ONCE(txq->trans_start);
> -
> -				if (time_after(jiffies, trans_start + dev->watchdog_timeo)) {
> -					timedout_ms = jiffies_to_msecs(jiffies - trans_start);
> +				timedout_ms = netif_xmit_timeout_ms(txq,
> +								    &trans_start);
> +				if (timedout_ms) {

The use of the new helper in the core feels a bit forced, I'd leave 
the core as is. Otherwise you need the awkward output param, and
core now duplicates the netif_xmit_stopped(txq) check

>  					atomic_long_inc(&txq->trans_timeout);
>  					break;
>  				}