From mboxrd@z Thu Jan  1 00:00:00 1970
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Date: Fri, 14 Nov 2008 09:22:44 +0100
From: Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>
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Subject: Re: [Xenomai-help] Mode switch when using RT heap on ARM
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To: Wolfgang Grandegger <wg@domain.hid>
Cc: xenomai-help <xenomai@xenomai.org>

Wolfgang Grandegger wrote:
> Gilles Chanteperdrix wrote:
>> Wolfgang Grandegger wrote:
>>> Hello,
>>>
>>> I realized that accessing memory allocated with rt_heap_alloc() causes
>>> mode switches on ARM i.mx31. The attached patch provides a demo program
>>> to demonstrate the problem, which actually does *not* show up on my
>>> PowerPC TQM5200 board.
>> Index: xenomai-2.4.x/examples/native/rtheap.c
>> ===================================================================
>> --- /dev/null
>> +++ xenomai-2.4.x/examples/native/rtheap.c
>> @@ -0,0 +1,164 @@
>> +#include <stdio.h>
>> +#include <signal.h>
>> +#include <unistd.h>
>> +#include <sys/mman.h>
>> +
>> +#include <native/task.h>
>> +#include <native/timer.h>
>> +#include <native/heap.h>
>> +
>> +#define USE_HEAP
>> +//#define USE_SIGXCPU
>> +
>> +#define HEAP_SIZE (1024*1024)
>> +#define HEAP_MODE 0		/* Local heap. */
>> +
>> +RT_HEAP heap_desc;
>> +RT_TASK demo_task;
>> +
>> +
>> +static int block_sizes[] = {16, 20, 90, 150, 310, 800, 1000};
>> +
>> +/* NOTE: error handling omitted. */
>> +
>> +void demo(void *arg)
>> +{
>> +	RTIME now, previous;
>> +	void *block;
>> +	int sizes = sizeof(block_sizes) / sizeof(int);
>> +	int count = 0;
>> +	int size, err;
>> +	int *ptr;
>> +
>> +#ifdef USE_SIGXCPU
>> +	/* Ask Xenomai to warn us upon switches to secondary mode. */
>> +	rt_task_set_mode(0, T_WARNSW, NULL);
>> +#endif
>> +
>> +	/*
>> +	 * Arguments: &task (NULL=self),
>> +	 *            start time,
>> +	 *            period (here: 1 s)
>> +	 */
>> +	rt_task_set_periodic(NULL, TM_NOW, 10000000);
>> +	previous = rt_timer_read();
>> +
>> +	while (1) {
>> +		rt_task_wait_period(NULL);
>> +		now = rt_timer_read();
>> +
>> +		size = block_sizes[count % sizes];
>> +#ifdef USE_HEAP
>> +		/*
>> +		 * Request a 16-bytes block, asking for a non-blocking call
>> +		 * since only Xenomai tasks may block.
>> +		 */
>> +		err = rt_heap_alloc(&heap_desc, size, TM_NONBLOCK, &block);
>> +		if (err) {
>> +			printf("rt_heap_alloc() failed with %d\n", err);
>> +			break;
>> +		}
>> +
>> +		ptr = (int *)block;
>> +		*ptr = 0xdeadbeef;
>> +		if (*ptr != 0xdeadbeef) {
>> +			printf("Write/read test to heap failed\n");
>> +			break;
>> +		}
>> +
>> +		ptr = (int *)(block + size - sizeof(int));
>>
>> This is not guaranteed to be aligned on an int. Could you try:
>>
>> 		ptr = (int *)(((unsigned long) block + size - sizeof(int)) & ~3);
> 
> With aligned accesses rtheap reports just3 mode switches in both modes,
> 0 and H_NONCACHED. But already one mode switch is too much!

I hope we get several mode switches because the allocator returns
different pages. To workaround this, we will have to cause a fault on
each page.  We can do this either in kernel or user-space.

-- 
					    Gilles.