netdev - Re: [PATCH 3/3] net: hisilicon: new hip04 ethernet driver

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Message-ID: <4392030.XayIa35sfH@wuerfel>
Date:	Tue, 25 Mar 2014 18:57:21 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Florian Fainelli <f.fainelli@...il.com>
Cc:	Zhangfei Gao <zhangfei.gao@...il.com>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	Mark Rutland <mark.rutland@....com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
	netdev <netdev@...r.kernel.org>,
	Zhangfei Gao <zhangfei.gao@...aro.org>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH 3/3] net: hisilicon: new hip04 ethernet driver

On Tuesday 25 March 2014 10:16:28 Florian Fainelli wrote:
> 
> Ok, well that's really unfortunate, to achieve the best of everything,
> the workaround should probably look like:
> 
> - keep reclaiming TX buffers in ndo_start_xmit() in case you push more
> packets to the NICs than your timer can free
> - reclaim TX buffers in NAPI poll() context for "symetrical" workloads
> where e.g: TCP ACKs received allow you to complete TX buffers
> - have a timer like you suggest which should help with transmit only
> workloads at a slow rate

Yes, that is what I was thinking, but with orphaning the tx skbs,
we can probably be a little smarter. Note that in order to check
the state of the queue, we have to do a read from uncached memory,
since the hardware also doesn't support cache coherent DMA.
We don't want to do that too often.

	Arnd
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