netdev - Re: netif_receive_skb_list and interrupts enabled/disabled

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Date:   Wed, 27 Mar 2019 09:20:11 +0100
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     Heiner Kallweit <hkallweit1@...il.com>
Cc:     Edward Cree <ecree@...arflare.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        brouer@...hat.com
Subject: Re: netif_receive_skb_list and interrupts enabled/disabled

On Tue, 26 Mar 2019 21:04:09 +0100
Heiner Kallweit <hkallweit1@...il.com> wrote:

> A question inspired by 0a25d92c6f4f ("dpaa2-eth: use netif_receive_skb_list"):
> kerneldoc of netif_receive_skb_list states that interrupts should be
> enabled. 

Do notice that the exact same comment (and rule) applies to
netif_receive_skb() which also have below comment:

/* [...]
 * This function may only be called from softirq context and interrupts
 * should be enabled.
 */

> When used from NAPI context irqs typically are disabled.
> And if the NAPI budget is fully consumed then interrupts don't get enabled
> in the same NAPI poll loop. How is this supposed to play together?

You have misunderstood that is means that interrupts should be
enabled.  It is talking about local_irq_disable/enable and
local_irq_save/restore.  This is different from disabling the IRQs on a
given NIC RX-queue.

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer