netdev - Re: [PATCH v5] net: ethernet: add driver for Aurora VLSI NB8800 Ethernet controller

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Date:	Wed, 11 Nov 2015 20:47:55 +0000
From:	Måns Rullgård <mans@...sr.com>
To:	David Miller <davem@...emloft.net>
Cc:	romieu@...zoreil.com, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, slash.tmp@...e.fr
Subject: Re: [PATCH v5] net: ethernet: add driver for Aurora VLSI NB8800 Ethernet controller

David Miller <davem@...emloft.net> writes:

> From: Måns Rullgård <mans@...sr.com>
> Date: Wed, 11 Nov 2015 19:35:05 +0000
>
>>> I don't think it's silly at all.
>> 
>> I'm sure I read somewhere that the time spent spinning on a lock should
>> be kept as small as possible.
>> 
>>> And unless you can measure it making a difference, don't knock the idea.
>> 
>> I tried using netif_tx_lock() in the IRQ handler instead, and it locked
>> up solid.  Clearly that was the wrong thing to do.
>
> Oh that's right, it's a BH lock not an IRQ one.
>
> Yet another argument for doing everything in ->poll(), thus making all
> operations outside of NAPI scheduling run in software interrupt
> context, and therefore being able to make use of the TXQ lock for
> this.

Well, I tried calling the DMA restart function from NAPI poll under
netif_tx_lock().  Now it works only as long as there is incoming
traffic.

-- 
Måns Rullgård
mans@...sr.com
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