netdev - Re: net: Detect drivers that reschedule NAPI and exhaust budget

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Message-ID: <1419098412.11185.8.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Sat, 20 Dec 2014 10:00:12 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	David Miller <davem@...emloft.net>, david.vrabel@...rix.com,
	netdev@...r.kernel.org, xen-devel@...ts.xenproject.org,
	konrad.wilk@...cle.com, boris.ostrovsky@...cle.com,
	edumazet@...gle.com
Subject: Re: net: Detect drivers that reschedule NAPI and exhaust budget

On Sat, 2014-12-20 at 17:55 +1100, Herbert Xu wrote:

> -- >8 --
> The commit d75b1ade567ffab085e8adbbdacf0092d10cd09c (net: less
> interrupt masking in NAPI) required drivers to leave poll_list
> empty if the entire budget is consumed.
> 
> We have already had two broken drivers so let's add a check for
> this.
> 
> Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>
> 
> diff --git a/net/core/dev.c b/net/core/dev.c
> index f411c28..47fdc5c 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -4620,7 +4620,13 @@ static void net_rx_action(struct softirq_action *h)
>  					 */
>  					napi_gro_flush(n, HZ >= 1000);
>  				}
> -				list_add_tail(&n->poll_list, &repoll);
> +				/* Some drivers may have called napi_schedule
> +				 * prior to exhausting their budget.
> +				 */
> +				if (unlikely(!list_empty(&n->poll_list)))
> +					pr_warn("%s: Budget exhausted after napi rescheduled\n", n->dev ? n->dev->name : "backlog");
> +				else
> +					list_add_tail(&n->poll_list, &repoll);
>  			}
>  		}
>  
> Thanks,

OK, but could you :
1) use pr_warn_once()
2) split the too long line
	pr_warn_once("%s: Budget exhausted after napi rescheduled\n",
		     n->dev ? n->dev->name : "backlog");

Thanks Herbert !


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