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

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Date:	Tue, 10 Nov 2015 21:11:21 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	mans@...sr.com
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

From: Måns Rullgård <mans@...sr.com>
Date: Wed, 11 Nov 2015 00:40:09 +0000

> When the DMA complete interrupt arrives, the next chain should be
> kicked off as quickly as possible, and I don't see why that would
> benefit from being done in napi context.

NAPI isn't about low latency, it's about fairness and interrupt
mitigation.

You probably don't even realize that all of the TX SKB freeing you do
in the hardware interrupt handler end up being actually processed by a
scheduled software interrupt anyways.

So you are gaining almost nothing by not doing TX completion in NAPI
context, whereas by doing so you would be gaining a lot including
more simplified locking or even the ability to do no locking at all.
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