netdev - Re: [PATCH] net: af_packet: Use hrtimer to do the retire operation

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Message-Id: <20250812170430.290604-1-jackzxcui1989@163.com>
Date: Wed, 13 Aug 2025 01:04:30 +0800
From: Xin Zhao <jackzxcui1989@....com>
To: willemdebruijn.kernel@...il.com,
	edumazet@...gle.com,
	ferenc@...es.dev
Cc: davem@...emloft.net,
	kuba@...nel.org,
	pabeni@...hat.com,
	horms@...nel.org,
	netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: af_packet: Use hrtimer to do the retire operation

On Mon, 2025-08-11 at 22:48 +0800, Willem wrote:

> > @@ -603,9 +603,10 @@ static void prb_setup_retire_blk_timer(struct packet_sock *po)
> >  	struct tpacket_kbdq_core *pkc;
> > 
> >  	pkc = GET_PBDQC_FROM_RB(&po->rx_ring);
> > -	timer_setup(&pkc->retire_blk_timer, prb_retire_rx_blk_timer_expired,
> > -		    0);
> > -	pkc->retire_blk_timer.expires = jiffies;
> > +	hrtimer_setup(&pkc->retire_blk_timer, prb_retire_rx_blk_timer_expired,
> > +		      CLOCK_MONOTONIC, HRTIMER_MODE_REL_SOFT);
> > +	if (pkc->tov_in_msecs == 0)
> > +		pkc->tov_in_msecs = jiffies_to_msecs(1);

> why is this bounds check needed now, while it was not needed when
> converting to jiffies?
> 
> init_prb_bdqc will compute a retire_blk_tov if it is passed as zero,
> by calling prb_calc_retire_blk_tmo.

Dear Willem,

I am very grateful for your suggestion. I will delete this bounds check in the v1
PATCH.


> >  static void _prb_refresh_rx_retire_blk_timer(struct tpacket_kbdq_core *pkc)
> >  {
> > -	mod_timer(&pkc->retire_blk_timer,
> > -			jiffies + pkc->tov_in_jiffies);
> > +	hrtimer_start_range_ns(&pkc->retire_blk_timer,
> > +			       ms_to_ktime(pkc->tov_in_msecs), 0, HRTIMER_MODE_REL_SOFT);

> Just hrtimer_start if leaving the slack (delta_ns) as 0.
> 
> More importantly, this scheduled the timer, while the caller also
> returns HRTIMER_RESTART. Should this just call hrtimer_set_expires or
> hrtimer_forward.

I will use hrtimer_set_expires here while using hrtimer_start in 
prb_setup_retire_blk_timer to start the timer.
Previously I used hrtimer_forward here, then encountered 
WARN_ON(timer->state & HRTIMER_STATE_ENQUEUED warning in the hrtimer_forward
function. This warning occurred because the tpacket_rcv function eventually calls
prb_open_block, which might call _prb_refresh_rx_retire_blk_timer at the same time
prb_retire_rx_blk_timer_expired might also call _prb_refresh_rx_retire_blk_timer,
leading to the warning.


> >  refresh_timer:
> >  	_prb_refresh_rx_retire_blk_timer(pkc);
> > +	ret = HRTIMER_RESTART;
> 
> reinitializing a variable that was already set to the same value?
> > 
> >  out:
> >  	spin_unlock(&po->sk.sk_receive_queue.lock);
> > +	return ret;
> 
> just return HRTIMER_RESTART directly.
> >  }

I will modify the patch based on these suggestions and upload it later.


Thanks
Xin Zhao