Skip to content

Commit

Permalink
freertos: Fix SMP round robin scheduling
Browse files Browse the repository at this point in the history 
The previous SMP freertos round robin would skip over tasks when
time slicing. This commit implements a Best Effort Round Robin
where selected tasks are put to the back of the list, thus
makes the time slicing more fair.

- Documentation has been updated accordingly.
- Tidy up vTaskSwitchContext() to match v10.4.3 more
- Increased esp_ipc task stack size to avoid overflow

Closes #7256
  • Loading branch information
@Dazza0
Dazza0 committed Nov 11, 2021
1 parent f6db715 commit 466c42c
Show file tree
Hide file tree
Showing 7 changed files with 388 additions and 205 deletions.
2 changes: 1 addition & 1 deletion components/esp_ipc/Kconfig
View file
Original file line number Diff line number Diff line change
Expand Up @@ -5,7 +5,7 @@ menu "IPC (Inter-Processor Call)"
range 512 65536 if !APPTRACE_ENABLE
range 2048 65536 if APPTRACE_ENABLE
default 2048 if APPTRACE_ENABLE
default 1024
default 1536
help
Configure the IPC tasks stack size. One IPC task runs on each core
(in dual core mode), and allows for cross-core function calls.
Expand Down
248 changes: 134 additions & 114 deletions components/freertos/tasks.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -143,6 +143,9 @@

/*-----------------------------------------------------------*/

#ifdef ESP_PLATFORM
#define taskSELECT_HIGHEST_PRIORITY_TASK() taskSelectHighestPriorityTaskSMP()
#else //ESP_PLATFORM
#define taskSELECT_HIGHEST_PRIORITY_TASK() \
{ \
UBaseType_t uxTopPriority = uxTopReadyPriority; \
Expand All @@ -159,6 +162,7 @@
listGET_OWNER_OF_NEXT_ENTRY( pxCurrentTCB[xPortGetCoreID()], &( pxReadyTasksLists[ uxTopPriority ] ) ); \
uxTopReadyPriority = uxTopPriority; \
} /* taskSELECT_HIGHEST_PRIORITY_TASK */
#endif //ESP_PLATFORM

/*-----------------------------------------------------------*/

Expand Down Expand Up @@ -3358,12 +3362,102 @@ BaseType_t xTaskIncrementTick( void )
#endif /* configUSE_APPLICATION_TASK_TAG */
/*-----------------------------------------------------------*/

void vTaskSwitchContext( void )
#ifdef ESP_PLATFORM
#if ( configUSE_PORT_OPTIMISED_TASK_SELECTION == 0 )
static void taskSelectHighestPriorityTaskSMP( void )
{
//Theoretically, this is only called from either the tick interrupt or the crosscore interrupt, so disabling
//interrupts shouldn't be necessary anymore. Still, for safety we'll leave it in for now.
int irqstate = portSET_INTERRUPT_MASK_FROM_ISR();
/* This function is called from a critical section. So some optimizations are made */
BaseType_t uxCurPriority;
BaseType_t xTaskScheduled = pdFALSE;
BaseType_t xNewTopPrioritySet = pdFALSE;
BaseType_t xCoreID = xPortGetCoreID(); /* Optimization: Read once */

/* Search for tasks, starting form the highest ready priority. If nothing is
* found, we eventually default to the IDLE tasks at priority 0 */
for ( uxCurPriority = uxTopReadyPriority; uxCurPriority >= 0 && xTaskScheduled == pdFALSE; uxCurPriority-- )
{
/* Check if current priority has one or more ready tasks. Skip if none */
if( listLIST_IS_EMPTY( &( pxReadyTasksLists[ uxCurPriority ] ) ) )
{
continue;
}

/* Save a copy of highest priority that has a ready state task */
if( xNewTopPrioritySet == pdFALSE )
{
xNewTopPrioritySet = pdTRUE;
uxTopReadyPriority = uxCurPriority;
}

/* We now search this priority's ready task list for a runnable task.
* We always start searching from the head of the list, so we reset
* pxIndex to point to the tail so that we start walking the list from
* the first item */
pxReadyTasksLists[ uxCurPriority ].pxIndex = ( ListItem_t * ) &( pxReadyTasksLists[ uxCurPriority ].xListEnd );

/* Get the first item on the list */
TCB_t * pxTCBCur;
TCB_t * pxTCBFirst;
listGET_OWNER_OF_NEXT_ENTRY( pxTCBCur, &( pxReadyTasksLists[ uxCurPriority ] ) );
pxTCBFirst = pxTCBCur;
do
{
/* Check if the current task is currently being executed. However, if
* it's being executed by the current core, we can still schedule it.
* Todo: Each task can store a xTaskRunState, instead of needing to
* check each core */
UBaseType_t ux;
for( ux = 0; ux < ( UBaseType_t )configNUM_CORES; ux++ )
{
if ( ux == xCoreID )
{
continue;
}
else if ( pxCurrentTCB[ux] == pxTCBCur )
{
/* Current task is already being executed. Get the next task */
goto get_next_task;
}
}

/* Check if the current task has a compatible affinity */
if ( ( pxTCBCur->xCoreID != xCoreID ) && ( pxTCBCur->xCoreID != tskNO_AFFINITY ) )
{
goto get_next_task;
}

/* The current task is runnable. Schedule it */
pxCurrentTCB[ xCoreID ] = pxTCBCur;
xTaskScheduled = pdTRUE;

/* Move the current tasks list item to the back of the list in order
* to implement best effort round robin. To do this, we need to reset
* the pxIndex to point to the tail again. */
pxReadyTasksLists[ uxCurPriority ].pxIndex = ( ListItem_t * ) &( pxReadyTasksLists[ uxCurPriority ].xListEnd );
uxListRemove( &( pxTCBCur->xStateListItem ) );
vListInsertEnd( &( pxReadyTasksLists[ uxCurPriority ] ), &( pxTCBCur->xStateListItem ) );
break;

get_next_task:
/* The current task cannot be scheduled. Get the next task in the list */
listGET_OWNER_OF_NEXT_ENTRY( pxTCBCur, &( pxReadyTasksLists[ uxCurPriority ] ) );
} while( pxTCBCur != pxTCBFirst); /* Check to see if we've walked the entire list */
}

assert( xTaskScheduled == pdTRUE ); /* At this point, a task MUST have been scheduled */
}
#endif /* configUSE_PORT_OPTIMISED_TASK_SELECTION */
#endif //ESP_PLATFORM

void vTaskSwitchContext( void )
{
#ifdef ESP_PLATFORM
/* vTaskSwitchContext is called either from:
* - ISR dispatcher when return from an ISR (interrupts will already be disabled)
* - vTaskSuspend() which is not in a critical section
* Therefore, we enter a critical section ISR version to ensure safety */
taskENTER_CRITICAL_ISR();
#endif // ESP_PLATFORM
if( uxSchedulerSuspended[ xPortGetCoreID() ] != ( UBaseType_t ) pdFALSE )
{
/* The scheduler is currently suspended - do not allow a context
Expand All @@ -3373,7 +3467,9 @@ void vTaskSwitchContext( void )
else
{
xYieldPending[ xPortGetCoreID() ] = pdFALSE;
#ifdef ESP_PLATFORM
xSwitchingContext[ xPortGetCoreID() ] = pdTRUE;
#endif // ESP_PLATFORM
traceTASK_SWITCHED_OUT();

#if ( configGENERATE_RUN_TIME_STATS == 1 )
Expand All @@ -3391,7 +3487,6 @@ void vTaskSwitchContext( void )
* overflows. The guard against negative values is to protect
* against suspect run time stat counter implementations - which
* are provided by the application, not the kernel. */
taskENTER_CRITICAL_ISR();
if( ulTotalRunTime > ulTaskSwitchedInTime[ xPortGetCoreID() ] )
{
pxCurrentTCB[ xPortGetCoreID() ]->ulRunTimeCounter += ( ulTotalRunTime - ulTaskSwitchedInTime[ xPortGetCoreID() ] );
Expand All @@ -3400,134 +3495,59 @@ void vTaskSwitchContext( void )
{
mtCOVERAGE_TEST_MARKER();
}
taskEXIT_CRITICAL_ISR();

ulTaskSwitchedInTime[ xPortGetCoreID() ] = ulTotalRunTime;
}
#endif /* configGENERATE_RUN_TIME_STATS */

/* Check for stack overflow, if configured. */
#ifdef ESP_PLATFORM
taskFIRST_CHECK_FOR_STACK_OVERFLOW();
taskSECOND_CHECK_FOR_STACK_OVERFLOW();
#else
taskCHECK_FOR_STACK_OVERFLOW();

/* Select a new task to run */

/*
We cannot do taskENTER_CRITICAL_ISR(); here because it saves the interrupt context to the task tcb, and we're
swapping that out here. Instead, we're going to do the work here ourselves. Because interrupts are already disabled, we only
need to acquire the mutex.
*/
vPortCPUAcquireMutex( &xTaskQueueMutex );

#if !configUSE_PORT_OPTIMISED_TASK_SELECTION
unsigned portBASE_TYPE foundNonExecutingWaiter = pdFALSE, ableToSchedule = pdFALSE, resetListHead;
unsigned portBASE_TYPE holdTop=pdFALSE;
tskTCB * pxTCB;

portBASE_TYPE uxDynamicTopReady = uxTopReadyPriority;
/*
* ToDo: This scheduler doesn't correctly implement the round-robin scheduling as done in the single-core
* FreeRTOS stack when multiple tasks have the same priority and are all ready; it just keeps grabbing the
* first one. ToDo: fix this.
* (Is this still true? if any, there's the issue with one core skipping over the processes for the other
* core, potentially not giving the skipped-over processes any time.)
*/

while ( ableToSchedule == pdFALSE && uxDynamicTopReady >= 0 )
{
resetListHead = pdFALSE;
// Nothing to do for empty lists
if (!listLIST_IS_EMPTY( &( pxReadyTasksLists[ uxDynamicTopReady ] ) )) {

ableToSchedule = pdFALSE;
tskTCB * pxRefTCB;

/* Remember the current list item so that we
can detect if all items have been inspected.
Once this happens, we move on to a lower
priority list (assuming nothing is suitable
for scheduling). Note: This can return NULL if
the list index is at the listItem */
pxRefTCB = pxReadyTasksLists[ uxDynamicTopReady ].pxIndex->pvOwner;

if ((void*)pxReadyTasksLists[ uxDynamicTopReady ].pxIndex==(void*)&pxReadyTasksLists[ uxDynamicTopReady ].xListEnd) {
//pxIndex points to the list end marker. Skip that and just get the next item.
listGET_OWNER_OF_NEXT_ENTRY( pxRefTCB, &( pxReadyTasksLists[ uxDynamicTopReady ] ) );
}

do {
listGET_OWNER_OF_NEXT_ENTRY( pxTCB, &( pxReadyTasksLists[ uxDynamicTopReady ] ) );
/* Find out if the next task in the list is
already being executed by another core */
foundNonExecutingWaiter = pdTRUE;
portBASE_TYPE i = 0;
for ( i=0; i<configNUM_CORES; i++ ) {
if (i == xPortGetCoreID()) {
continue;
} else if (pxCurrentTCB[i] == pxTCB) {
holdTop=pdTRUE; //keep this as the top prio, for the other CPU
foundNonExecutingWaiter = pdFALSE;
break;
}
}

if (foundNonExecutingWaiter == pdTRUE) {
/* If the task is not being executed
by another core and its affinity is
compatible with the current one,
prepare it to be swapped in */
if (pxTCB->xCoreID == tskNO_AFFINITY) {
pxCurrentTCB[xPortGetCoreID()] = pxTCB;
ableToSchedule = pdTRUE;
} else if (pxTCB->xCoreID == xPortGetCoreID()) {
pxCurrentTCB[xPortGetCoreID()] = pxTCB;
ableToSchedule = pdTRUE;
} else {
ableToSchedule = pdFALSE;
holdTop=pdTRUE; //keep this as the top prio, for the other CPU
}
} else {
ableToSchedule = pdFALSE;
}

if (ableToSchedule == pdFALSE) {
resetListHead = pdTRUE;
} else if ((ableToSchedule == pdTRUE) && (resetListHead == pdTRUE)) {
tskTCB * pxResetTCB;
do {
listGET_OWNER_OF_NEXT_ENTRY( pxResetTCB, &( pxReadyTasksLists[ uxDynamicTopReady ] ) );
} while(pxResetTCB != pxRefTCB);
}
} while ((ableToSchedule == pdFALSE) && (pxTCB != pxRefTCB));
} else {
if (!holdTop) --uxTopReadyPriority;
/* Before the currently running task is switched out, save its errno. */
#if ( configUSE_POSIX_ERRNO == 1 )
{
pxCurrentTCB->iTaskErrno = FreeRTOS_errno;
}
--uxDynamicTopReady;
}

#else
//For Unicore targets we can keep the current FreeRTOS O(1)
//Scheduler. I hope to optimize better the scheduler for
//Multicore settings -- This will involve to create a per
//affinity ready task list which will impact hugely on
//tasks module
taskSELECT_HIGHEST_PRIORITY_TASK();
#endif
#endif // ESP_PLATFORM

/* Select a new task to run using either the generic C or port
* optimised asm code. */
taskSELECT_HIGHEST_PRIORITY_TASK(); /*lint !e9079 void * is used as this macro is used with timers and co-routines too. Alignment is known to be fine as the type of the pointer stored and retrieved is the same. */
traceTASK_SWITCHED_IN();
xSwitchingContext[ xPortGetCoreID() ] = pdFALSE;

#ifdef ESP_PLATFORM
//Exit critical region manually as well: release the mux now, interrupts will be re-enabled when we
//exit the function.
vPortCPUReleaseMutex( &xTaskQueueMutex );
#endif // ESP_PLATFORM

xSwitchingContext[ xPortGetCoreID() ] = pdFALSE;
#if CONFIG_FREERTOS_WATCHPOINT_END_OF_STACK
vPortSetStackWatchpoint(pxCurrentTCB[xPortGetCoreID()]->pxStack);
#endif
#else
/* After the new task is switched in, update the global errno. */
#if ( configUSE_POSIX_ERRNO == 1 )
{
FreeRTOS_errno = pxCurrentTCB->iTaskErrno;
}
#endif

#if ( configUSE_NEWLIB_REENTRANT == 1 )
{
/* Switch Newlib's _impure_ptr variable to point to the _reent
* structure specific to this task.
* See the third party link http://www.nadler.com/embedded/newlibAndFreeRTOS.html
* for additional information. */
_impure_ptr = &( pxCurrentTCB->xNewLib_reent );
}
#endif /* configUSE_NEWLIB_REENTRANT */
#endif // ESP_PLATFORM
}
portCLEAR_INTERRUPT_MASK_FROM_ISR(irqstate);
#ifdef ESP_PLATFORM
/* Exit the critical section previously entered */
taskEXIT_CRITICAL_ISR();
#endif // ESP_PLATFORM
}
/*-----------------------------------------------------------*/

Expand Down
Loading

0 comments on commit 466c42c

Please sign in to comment.