netdev - Re: [PATCH net-next] net: flush the softnet backlog in process context

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Message-ID: <1472135557.14381.130.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Thu, 25 Aug 2016 07:32:37 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Paolo Abeni <pabeni@...hat.com>
Cc:     netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Tom Herbert <tom@...bertland.com>,
        Hannes Frederic Sowa <hannes@...essinduktion.org>
Subject: Re: [PATCH net-next] net: flush the softnet backlog in process
 context

On Thu, 2016-08-25 at 15:58 +0200, Paolo Abeni wrote:
> Currently in process_backlog(), the process_queue dequeuing is
> performed with local IRQ disabled, to protect against
> flush_backlog(), which runs in hard IRQ context.

Acked-by: Eric Dumazet <edumazet@...gle.com>

> @@ -6707,7 +6735,7 @@ static void rollback_registered_many(struct list_head *head)
>  		unlist_netdevice(dev);
>  
>  		dev->reg_state = NETREG_UNREGISTERING;
> -		on_each_cpu(flush_backlog, dev, 1);
> +		flush_all_backlogs(dev);
>  	}
>  
>  	synchronize_net();

In a future patch, we could change this so that we kick
flush_all_backlogs() once for all devices, instead of one device at a
time.

We would not pass @dev anymore as a parameter and simply look at
skb->dev->reg_state to decide to remove packets from queues in
flush_backlog()

Batching matters for some guys using hundred of devices and suddenly
removing them all in one go.

Thanks.