Re: [Xenomai-help] Mode switch when using RT heap on ARM

[Wolfgang Grandegger <wg@domain.hid>]

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!

Wolfgang.