linux-kernel - Re: [PATCH] atmel_tc clocksource/clockevent code

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Message-ID: <alpine.LFD.1.00.0803051742190.3099@apollo.tec.linutronix.de>
Date:	Wed, 5 Mar 2008 17:45:34 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Remy Bohmer <linux@...mer.net>
cc:	David Brownell <david-b@...bell.net>,
	Haavard Skinnemoen <hskinnemoen@...el.com>,
	akpm@...ux-foundation.org, LKML <linux-kernel@...r.kernel.org>,
	David Brownell <dbrownell@...rs.sourceforge.net>,
	Nicolas Ferre <nicolas.ferre@....atmel.com>,
	Andrew Victor <linux@...im.org.za>,
	john stultz <johnstul@...ibm.com>
Subject: Re: [PATCH] atmel_tc clocksource/clockevent code

On Wed, 5 Mar 2008, Remy Bohmer wrote:
> Hello David,
> 
> > Could you elaborate on where that 50-100 usec gets spent?
> 
> Attached I have put a screendump of my ETM debugger. It shows a
> complete flow of kernel function-calls of what happens on a timer
> interrupt. In this example the complete sequence takes about 154 us.
> Notice that the ETM is non-intrusive, and that the times are real and
> accurate in this trace. (you can even see the effects of CPU-caches,
> sometimes the same code just runs faster)

Is there any chance to convert this to a text table? Following that
png is pretty hard.

> So, hires timestamps -> really really welcome.
> hires timers -> there should be a (configurable) minimal resolution
> that fits the hardware to not overload the CPU.

clockevents let you set a minimum delta already. This can be set at
runtime before registering the device.

Thanks,

	tglx
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