netdev - Re: [PATCH net-next 0/2] sunvnet: Packet processing in non-interrupt context.

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Message-Id: <20141001.155009.2277009117294992988.davem@davemloft.net>
Date:	Wed, 01 Oct 2014 15:50:09 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	sowmini.varadhan@...cle.com
Cc:	raghuram.kothakota@...cle.com, netdev@...r.kernel.org
Subject: Re: [PATCH net-next 0/2] sunvnet: Packet processing in
 non-interrupt context.

From: Sowmini Varadhan <sowmini.varadhan@...cle.com>
Date: Wed, 1 Oct 2014 14:56:04 -0400

> 
> The existing sunvnet implementation does all the packet interception
> in LDC interrupt context. Patch 1 of this series moves the data
> processing to a bottom-half handler.
> 
> Some context for the reasons for choosing a BH handler over NAPI:
>    A NAPI (or simple tasklet) based implementation provides softirq
>    context, which allows the driver to safely invoke netif_receive_skb()
>    to deliver the packet to the IP stack. But in the case of sunvnet,
>    we are already receiving multiple packets for a single ldc_rx
>    interrupt, so the budget-based softirq-vs-polling infra does not
>    provide a significant optimization. Rather, it can get in the way,
>    if we constrain the vnet-rx path to a poorly chosen budget, and force
>    ourselves to send a STOPPED/START ldc exchange needlessly.
> 
>    A BH Rx handler is a simpler way to  avoid the weaknesses of processing
>    packets in LDC interrupt context, and also provides Rx load-spreading
>    across multiple CPUs.

I think you want to re-evaluate this considering napi_gro_receive() which
is what you should really be calling in a NAPI driver.
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