linux-kernel - Re: High resolution timers on AT91SAM926x

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Date:	Mon, 3 Mar 2008 17:29:18 -0800
From:	David Brownell <david-b@...bell.net>
To:	"Bosko Radivojevic" <bosko.radivojevic@...il.com>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	linux-rt-users@...r.kernel.org, tglx@...utronix.de
Subject: Re: High resolution timers on AT91SAM926x

On Monday 03 March 2008, Bosko Radivojevic wrote:
> I had CONFIG_ATMEL_TCLIB enabled, but not TCB_CLKSRC and
> TCB_CLKSRC_BLOCK=0. With all those options, I finally have HRT
> functionality. But, strange thing is that jitter of my little example
> (get time, sleep 1ms, get time, show the difference) is around 250us.
> Maybe this is normal for this architecture?

I have no idea why that would be.  Maybe you can find out.  :)


> System is (as noted on rt.wik site) very slow with NO_HZ option enabled.

It doesn't exactly say *why* or compare to other arm926ejs
chips ... 

Could the 64-bit math (ktime stuff) be a factor there?  Your
board probably only runs at 95 (or-so) bogomips after all.

And is that just a NO_HZ issue, or generically an issue when
oneshot timer modes are in heavy use?

- Dave
 
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