Re: [RFC v3] net/core: add optional threading for backlog processing

[Felix Fietkau]

On 20.02.23 01:41, Hillf Danton wrote:
> On Sun, 19 Feb 2023 14:10:05 +0100 Felix Fietkau <nbd@xxxxxxxx>
> >  /* Network device is going away, flush any packets still pending */
> >  static void flush_backlog(struct work_struct *work)
> >  {
> > +	unsigned int process_queue_empty;
> > +	bool threaded, flush_processq;
> >  	struct sk_buff *skb, *tmp;
> >  	struct softnet_data *sd;
> >  
> > @@ -5792,8 +5794,15 @@ static void flush_backlog(struct work_struct *work)
> >  			input_queue_head_incr(sd);
> >  		}
> >  	}
> > +
> > +	threaded = test_bit(NAPI_STATE_THREADED, &sd->backlog.state);
> > +	flush_processq = threaded &&
> > +			 !skb_queue_empty_lockless(&sd->process_queue);
> >  	rps_unlock_irq_enable(sd);
> >  
> > +	if (threaded)
> > +		goto out;
> > +
> >  	skb_queue_walk_safe(&sd->process_queue, skb, tmp) {
> >  		if (skb->dev->reg_state == NETREG_UNREGISTERING) {
> >  			__skb_unlink(skb, &sd->process_queue);
> > @@ -5801,7 +5810,16 @@ static void flush_backlog(struct work_struct *work)
> >  			input_queue_head_incr(sd);
> >  		}
> >  	}
> > +
> > +out:
> >  	local_bh_enable();
> > +
> > +	while (flush_processq) {
> > +		msleep(1);
> > +		rps_lock_irq_disable(sd);
> > +		flush_processq = process_queue_empty == sd->process_queue_empty;
> > +		rps_unlock_irq_enable(sd);
> > +	}
> >  }
>
> Have hard time guessing how this wait works given process_queue_empty
> not initialized. Is this random check intended?
Please check my initial reply to this patch. I forgot to amend the 
commit with the missing initialization lines before sending out the patch.

- Felix