netdev - Re: [PATCH (sh-2.6) 1/4] clksource: Generic timer infrastructure

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Date:	Thu, 3 Mar 2011 14:55:24 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Peppe CAVALLARO <peppe.cavallaro@...com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Stuart MENEFY <stuart.menefy@...com>,
	"linux-sh@...r.kernel.org" <linux-sh@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	John Stultz <johnstul@...ibm.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>
Subject: Re: [PATCH (sh-2.6) 1/4] clksource: Generic timer infrastructure

On Thursday 03 March 2011, Peppe CAVALLARO wrote:
> This logic is already in the driver, indeed.
> What I've seen on our embedded systems is that the
> cost of RX interrupts is very hight and NAPI partially helps.
> Typically, in an IP-STB, I receive a burst of UDP pkt
> and this  means that many interrupts occur (~99% of CPU
> usage on slow platforms).
> With the ext timer I was able to reduce the CPU usage in
> these kind of scenarios to ~50%.

I don't understand. Shouldn't the interrupts be stopped as long
as the system is busy? This sounds like a bug in your NAPI
handling, or maybe you just need to use a lower NAPI_WEIGHT
so you stay in polling mode longer.

	Arnd
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