On 06/23/2011 01:36 PM, Jan Kiszka wrote:
> On 2011-06-23 13:29, Gilles Chanteperdrix wrote:
>> On 06/23/2011 11:09 AM, Jan Kiszka wrote:
>>> On 2011-06-23 11:05, Gilles Chanteperdrix wrote:
>>>> On 06/23/2011 09:38 AM, Jan Kiszka wrote:
>>>>>> +#ifdef CONFIG_XENO_FASTSYNCH
>>>>>> + if (xeno_get_current() != XN_NO_HANDLE &&
>>>>>> + !(xeno_get_current_mode() & XNRELAX) && buf_pool_get()) {
>>>>>> + struct print_buffer *old;
>>>>>> +
>>>>>> + old = buf_pool_get();
>>>>>> + while (old != buffer) {
>>>>>> + buffer = old;
>>>>>> + old = buf_pool_cmpxchg(buffer,
>>>>>> buffer->pool_next);
>>>>>
>>>>> Though unlikely, it's still possible: The buffer obtained in the last
>>>>> round may have been dequeued meanwhile and then freed (in case a third
>>>>> buffer was released to the pool, filling it up to pool_capacity).
>>>>
>>>> I do not get it: it seems to me that if the current head (that is
>>>> buf_pool_get()) is freed, then the cmpxchg will fail, so we will loop
>>>> and try again.
>>>
>>> Problematic is the dereferencing of the stale buffer pointer obtained
>>> during the last cmpxchg or via buf_pool_get. This happens before the new
>>> cmpxchg.
>>
>> Ok. Got it, that would be a problem only if the stale pointer pointed to
>> an unmapped area, but ok, better avoid freeing the buffers. I guess it
>> would not be a problem as applications tend to have a fixed number of
>> threads anyway.
>
> That is a risky assumption, proven wrong e.g. by one of our
> applications. Threads may always be created or destroyed depending on
> the mode of an application, specifically if it is a larger one.
Here is another attempt, based on a bitmap.
diff --git a/src/rtdk/rt_print.c b/src/rtdk/rt_print.c
index 93b711a..fb4820f 100644
--- a/src/rtdk/rt_print.c
+++ b/src/rtdk/rt_print.c
@@ -28,7 +28,9 @@
#include <syslog.h>
#include <rtdk.h>
+#include <nucleus/types.h> /* For BITS_PER_LONG */
#include <asm/xenomai/system.h>
+#include <asm/xenomai/atomic.h> /* For atomic_cmpxchg */
#include <asm-generic/stack.h>
#define RT_PRINT_BUFFER_ENV "RT_PRINT_BUFFER"
@@ -37,6 +39,9 @@
#define RT_PRINT_PERIOD_ENV "RT_PRINT_PERIOD"
#define RT_PRINT_DEFAULT_PERIOD 100 /* ms */
+#define RT_PRINT_BUFFERS_COUNT_ENV "RT_PRINT_BUFFERS_COUNT"
+#define RT_PRINT_DEFAULT_BUFFERS_COUNT 4
+
#define RT_PRINT_LINE_BREAK 256
#define RT_PRINT_SYSLOG_STREAM NULL
@@ -75,6 +80,12 @@ static pthread_mutex_t buffer_lock;
static pthread_cond_t printer_wakeup;
static pthread_key_t buffer_key;
static pthread_t printer_thread;
+#ifdef CONFIG_XENO_FASTSYNCH
+static xnarch_atomic_t *pool_bitmap;
+static unsigned pool_bitmap_len;
+static unsigned pool_buf_size;
+static unsigned long pool_start, pool_len;
+#endif /* CONFIG_XENO_FASTSYNCH */
static void cleanup_buffer(struct print_buffer *buffer);
static void print_buffers(void);
@@ -243,10 +254,36 @@ static void set_buffer_name(struct print_buffer *buffer,
const char *name)
}
}
+void rt_print_init_inner(struct print_buffer *buffer, size_t size)
+{
+ buffer->size = size;
+
+ memset(buffer->ring, 0, size);
+
+ buffer->read_pos = 0;
+ buffer->write_pos = 0;
+
+ buffer->prev = NULL;
+
+ pthread_mutex_lock(&buffer_lock);
+
+ buffer->next = first_buffer;
+ if (first_buffer)
+ first_buffer->prev = buffer;
+ first_buffer = buffer;
+
+ buffers++;
+ pthread_cond_signal(&printer_wakeup);
+
+ pthread_mutex_unlock(&buffer_lock);
+}
+
int rt_print_init(size_t buffer_size, const char *buffer_name)
{
struct print_buffer *buffer = pthread_getspecific(buffer_key);
size_t size = buffer_size;
+ unsigned long old_bitmap;
+ unsigned j;
if (!size)
size = default_buffer_size;
@@ -260,39 +297,56 @@ int rt_print_init(size_t buffer_size, const char
*buffer_name)
return 0;
}
cleanup_buffer(buffer);
+ buffer = NULL;
}
- buffer = malloc(sizeof(*buffer));
- if (!buffer)
- return ENOMEM;
+#ifdef CONFIG_XENO_FASTSYNCH
+ /* Find a free buffer in the pool */
+ do {
+ unsigned long bitmap;
+ unsigned i;
- buffer->ring = malloc(size);
- if (!buffer->ring) {
- free(buffer);
- return ENOMEM;
- }
- memset(buffer->ring, 0, size);
+ for (i = 0; i < pool_bitmap_len; i++) {
+ old_bitmap = xnarch_atomic_get(&pool_bitmap[i]);
+ if (old_bitmap)
+ goto acquire;
+ }
- buffer->read_pos = 0;
- buffer->write_pos = 0;
+ goto not_found;
- buffer->size = size;
+ acquire:
+ do {
+ bitmap = old_bitmap;
+ j = __builtin_ffsl(bitmap) - 1;
+ old_bitmap = xnarch_atomic_cmpxchg(&pool_bitmap[i],
+ bitmap,
+ bitmap & ~(1UL <<
j));
+ } while (old_bitmap != bitmap && old_bitmap);
+ j += i * BITS_PER_LONG;
+ } while (!old_bitmap);
- set_buffer_name(buffer, buffer_name);
+ buffer = (struct print_buffer *)(pool_start + j * pool_buf_size);
- buffer->prev = NULL;
+ not_found:
+#endif /* CONFIG_XENO_FASTSYNCH */
- pthread_mutex_lock(&buffer_lock);
+ if (!buffer) {
+ assert_nrt();
- buffer->next = first_buffer;
- if (first_buffer)
- first_buffer->prev = buffer;
- first_buffer = buffer;
+ buffer = malloc(sizeof(*buffer));
+ if (!buffer)
+ return ENOMEM;
- buffers++;
- pthread_cond_signal(&printer_wakeup);
+ buffer->ring = malloc(size);
+ if (!buffer->ring) {
+ free(buffer);
+ return ENOMEM;
+ }
- pthread_mutex_unlock(&buffer_lock);
+ rt_print_init_inner(buffer, size);
+ }
+
+ set_buffer_name(buffer, buffer_name);
pthread_setspecific(buffer_key, buffer);
@@ -346,12 +400,44 @@ static void cleanup_buffer(struct print_buffer *buffer)
{
struct print_buffer *prev, *next;
+ assert_nrt();
+
pthread_setspecific(buffer_key, NULL);
pthread_mutex_lock(&buffer_lock);
print_buffers();
+ pthread_mutex_unlock(&buffer_lock);
+
+#ifdef CONFIG_XENO_FASTSYNCH
+ /* Return the buffer to the pool */
+ {
+ unsigned long old_bitmap, bitmap;
+ unsigned i, j;
+
+ if ((unsigned long)buffer - pool_start >= pool_len)
+ goto dofree;
+
+ j = ((unsigned long)buffer - pool_start) / pool_buf_size;
+ i = j / BITS_PER_LONG;
+ j = j % BITS_PER_LONG;
+
+ old_bitmap = xnarch_atomic_get(&pool_bitmap[i]);
+ do {
+ bitmap = old_bitmap;
+ old_bitmap = xnarch_atomic_cmpxchg(&pool_bitmap[i],
+ bitmap,
+ bitmap | (1UL << j));
+ } while (old_bitmap != bitmap);
+
+ return;
+ }
+ dofree:
+#endif /* CONFIG_XENO_FASTSYNCH */
+
+ pthread_mutex_lock(&buffer_lock);
+
prev = buffer->prev;
next = buffer->next;
@@ -523,6 +609,64 @@ void __rt_print_init(void)
print_period.tv_sec = period / 1000;
print_period.tv_nsec = (period % 1000) * 1000000;
+#ifdef CONFIG_XENO_FASTSYNCH
+ /* Fill the buffer pool */
+ {
+ unsigned buffers_count, i;
+
+ buffers_count = RT_PRINT_DEFAULT_BUFFERS_COUNT;
+
+ value_str = getenv(RT_PRINT_BUFFERS_COUNT_ENV);
+ if (value_str) {
+ errno = 0;
+ buffers_count = strtoul(value_str, NULL, 0);
+ if (errno) {
+ fprintf(stderr, "Invalid %s\n",
+ RT_PRINT_BUFFERS_COUNT_ENV);
+ exit(1);
+ }
+ }
+
+ pool_bitmap_len = (buffers_count + BITS_PER_LONG - 1)
+ / BITS_PER_LONG;
+ if (!pool_bitmap_len)
+ goto done;
+
+ pool_bitmap = malloc(pool_bitmap_len * sizeof(*pool_bitmap));
+ if (!pool_bitmap) {
+ fprintf(stderr, "Error allocating rt_printf "
+ "buffers\n");
+ exit(1);
+ }
+
+ pool_buf_size = sizeof(struct print_buffer) +
default_buffer_size;
+ pool_len = buffers_count * pool_buf_size;
+ pool_start = (unsigned long)malloc(pool_len);
+ if (!pool_start) {
+ fprintf(stderr, "Error allocating rt_printf "
+ "buffers\n");
+ exit(1);
+ }
+
+ for (i = 0; i < buffers_count / BITS_PER_LONG; i++)
+ xnarch_atomic_set(&pool_bitmap[i], ~0UL);
+ if (buffers_count % BITS_PER_LONG)
+ xnarch_atomic_set(&pool_bitmap[i],
+ (1UL << (buffers_count %
BITS_PER_LONG)) - 1);
+
+ for (i = 0; i < buffers_count; i++) {
+ struct print_buffer *buffer =
+ (struct print_buffer *)
+ (pool_start + i * pool_buf_size);
+
+ buffer->ring = (char *)(buffer + 1);
+
+ rt_print_init_inner(buffer, default_buffer_size);
+ }
+ }
+ done:
+#endif /* CONFIG_XENO_FASTSYNCH */
+
pthread_mutex_init(&buffer_lock, NULL);
pthread_key_create(&buffer_key, (void (*)(void*))cleanup_buffer);
--
Gilles.
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