linux-kernel - Re: realtime-preempt and arm

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Date:	Fri, 01 Dec 2006 00:56:08 +0900 (JST)
From:	junjiec@...il.com
To:	tike64@...oo.com
Cc:	linux-kernel@...r.kernel.org
Subject: Re: realtime-preempt and arm

Hi,

Without the support of High Resolution Timer supported,
the timer resolution wouldn't change.
With high-resolution-timer supported,
our arm926-based board could get resolution like 40~50us.
There are codes you can reference ,may be you should just try to implement it.

JFI, Thanks.

From: tike64 <tike64@...oo.com>
Subject: realtime-preempt and arm
Date: Wed, 29 Nov 2006 00:57:05 -0800 (PST)

> Hi all,
> 
> I'm trying the realtime-preempt patch-2.6.18-rt6 on
> lh7a400 arm system with little success. In a test
> program I try 5 ms timeout with select() but get 20 ms
> avg or 26 ms max. When the framebuffer scrolls, the
> max delay goes up to 59 ms. With a vanilla kernel I
> get 10 ms (because of tick resolution?), 11 ms and 39
> ms.
> 
> My question is, is the realtime-preempt patch supposed
> to work on arm architecture and/or without high
> resolution timer (which lh7a40x seems to lack) at all
> or should I just try to be more clever.
> 
> Relevant code:
> 
> ====
> prio.sched_priority = 99;
> if (sched_setscheduler(0, SCHED_RR, &prio) < 0) ...
> if (mlockall(MCL_CURRENT | MCL_FUTURE) < 0) ...
> while (1) {
> 	t = raw_timer();
> 	tv.tv_usec = 5000;
> 	tv.tv_sec = 0;
> 	select(0, 0, 0, 0, &tv);
> 	t = raw_timer() - t;
> 	if (max_t < t) max_t = t;
> 	if (min_t > t) min_t = t;
> 	avg_t += t;
> 	++n;
> 	if (n < 100) continue;
> 	printf("%i revs; min: %i max: %i avg: %i\n",
> 		n,
> 		min_t,
> 		max_t,
> 		(avg_t + n / 2) / n);
> ====
> 
> Relevant config: PREEMPT_RT, PREEMPT_SOFTIRQS,
> PREEMPT_HARDIRQS
> 
> I didnt' enable HIGH_RES_TIMERS because lh7a40x seems
> not to support it.
> 
> --
> 
> tike
> 
> 
> 
>  
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