Re: [Xen-devel] net: Detect drivers that reschedule NAPI and exhaust budget

[Eric Dumazet <eric.dumazet@xxxxxxxxx>]

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@xxxxxxxxxxxxxxxxxxx>
> 
> 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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