Commit 475d5eb8 authored by Cedric Roux's avatar Cedric Roux

T: bug fixes for the T cache

- 'busy' has to be handled in a more atomic fashion to avoid crazy
  runtime race conditions
- the basic simulator is too fast sometimes; rewrite the accesses to
  the T cache to avoid there again crazy behaviors

Hopefully that's better...
parent d4a8b5f3
Pipeline #10298 failed with stage
in 0 seconds
......@@ -31,6 +31,12 @@ volatile int _T_freelist_head;
volatile int *T_freelist_head = &_T_freelist_head;
T_cache_t *T_cache;
#if BASIC_SIMULATOR
/* global variables used by T_GET_SLOT, see in T.h */
volatile uint64_t T_next_id;
volatile uint64_t T_active_id;
#endif
static void get_message(int s)
{
char t;
......
......@@ -112,13 +112,37 @@ extern volatile int *T_freelist_head;
extern T_cache_t *T_cache;
extern int *T_active;
/* When running the basic simulator, we may fill the T cache too fast.
* Let's not crash if it's full, just wait.
* Let's serialize write accesses to the T cache. For that, we use a
* 'ticket' mechanism. To acquire a T slot the caller needs to own the
* current active ticket. We also wait for the slot to be free if
* it is already in use.
*/
#if BASIC_SIMULATOR
# define T_BASIC_SIMULATOR_WAIT \
while (T_cache[T_LOCAL_slot].busy) usleep(100)
# define T_GET_SLOT \
do { \
extern volatile uint64_t T_next_id; \
extern volatile uint64_t T_active_id; \
uint64_t id; \
/* get a ticket */ \
id = __sync_fetch_and_add(&T_next_id, 1); \
/* wait for our turn */ \
while (id != __sync_fetch_and_add(&T_active_id, 0)) /* busy wait */; \
/* this is our turn, try to acquire the slot until it's free */ \
do { \
T_LOCAL_busy = __sync_fetch_and_or(&T_cache[T_LOCAL_slot].busy, 0x01); \
if (T_LOCAL_busy & 0x01) usleep(100); \
} while (T_LOCAL_busy & 0x01); \
/* check that there are still some tickets */ \
if (__sync_fetch_and_add(&T_active_id, 0) == 0xffffffffffffffff) { \
printf("T: reached the end of times, bye...\n"); \
abort(); \
} \
/* free our ticket, which signals the next waiter that it's its turn */ \
(void)__sync_fetch_and_add(&T_active_id, 1); \
} while (0)
#else
# define T_BASIC_SIMULATOR_WAIT /* */
# define T_GET_SLOT \
T_LOCAL_busy = __sync_fetch_and_or(&T_cache[T_LOCAL_slot].busy, 0x01);
#endif
/* used at header of Tn, allocates buffer */
......@@ -126,11 +150,12 @@ extern int *T_active;
char *T_LOCAL_buf; \
int T_LOCAL_size = 0; \
int T_LOCAL_slot; \
int T_LOCAL_busy; \
T_LOCAL_slot = __sync_fetch_and_add(T_freelist_head, 1) \
& (T_CACHE_SIZE - 1); \
(void)__sync_fetch_and_and(T_freelist_head, T_CACHE_SIZE - 1); \
T_BASIC_SIMULATOR_WAIT; \
if (T_cache[T_LOCAL_slot].busy) { \
T_GET_SLOT; \
if (T_LOCAL_busy & 0x01) { \
printf("%s:%d:%s: T cache is full - consider increasing its size\n", \
__FILE__, __LINE__, __FUNCTION__); \
abort(); \
......@@ -142,7 +167,7 @@ extern int *T_active;
#define T_COMMIT() \
T_cache[T_LOCAL_slot].length = T_LOCAL_size; \
__sync_synchronize(); \
T_cache[T_LOCAL_slot].busy = 1; \
(void)__sync_fetch_and_or(&T_cache[T_LOCAL_slot].busy, 0x02);
#define T_CHECK_SIZE(len, argnum) \
if (T_LOCAL_size + (len) > T_BUFFER_MAX) { \
......
......@@ -31,6 +31,10 @@
#endif
typedef struct {
/* 'busy' is a bit field
* bit 0: 1 means that slot is acquired by writer
* bit 1: 1 means that slot is ready for consumption
*/
volatile int busy;
char buffer[T_BUFFER_MAX];
int length;
......
......@@ -337,7 +337,7 @@ static void forward(void *_forwarder, char *buf, int size)
static void wait_message(void)
{
while (T_local_cache[T_busylist_head].busy == 0) usleep(1000);
while ((T_local_cache[T_busylist_head].busy & 0x02) == 0) usleep(1000);
}
void T_local_tracer_main(int remote_port, int wait_for_tracer,
......
Markdown is supported
0% or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment