On 04/08/2020 17:57, Gedare Bloom wrote:
On Tue, Aug 4, 2020 at 8:14 AM Richi Dubey<richidu...@gmail.com> wrote:
Hi,
I have a quick doubt about the logic in the else part of the
_Scheduler_SMP_Schedule_highest_ready function.
I'll give my understanding. Only Sebastian really understands this stuff;)
We get the action == SCHEDULER_TRY_TO_SCHEDULE_DO_BLOCK if the node returned by
get_highest_ready is already SCHEDULED and has a pinning level of 1 (or <=1).
This means that the highest ready eligible node is already scheduled and pinned to
a processor.
This means that the highest ready node cannot be scheduled right now,
for some reason. It is the thread that is already scheduled, or the
node is busy helping.
Why do we then change its state to BLOCKED and remove it from the chain of
ready nodes?
If the thread that owns the node can't be scheduled right now (e.g.,
it is already scheduled on a different node), then the node should be
blocked so we can maybe pick a different node to schedule.
Yes. I tried to improve the documentation a bit:
https://lists.rtems.org/pipermail/devel/2020-August/061144.html
What can be a bit confusing is that we have a scheduled state for
threads and for scheduler nodes:
/**
* @brief The thread state with respect to the scheduler.
*/
typedef enum {
/**
* @brief This thread is blocked with respect to the scheduler.
*
* This thread uses no scheduler nodes.
*/
THREAD_SCHEDULER_BLOCKED,
/**
* @brief This thread is scheduled with respect to the scheduler.
*
* This thread executes using one of its scheduler nodes. This could
be its
* own scheduler node or in case it owns resources taking part in the
* scheduler helping protocol a scheduler node of another thread.
*/
THREAD_SCHEDULER_SCHEDULED,
/**
* @brief This thread is ready with respect to the scheduler.
*
* None of the scheduler nodes of this thread is scheduled.
*/
THREAD_SCHEDULER_READY
} Thread_Scheduler_state;
/**
* @brief SMP scheduler node states.
*/
typedef enum {
/**
* @brief This scheduler node is blocked.
*
* A scheduler node is blocked if the corresponding thread is not ready.
*/
SCHEDULER_SMP_NODE_BLOCKED,
/**
* @brief The scheduler node is scheduled.
*
* A scheduler node is scheduled if the corresponding thread is ready
and the
* scheduler allocated a processor for it. A scheduled node is
assigned to
* exactly one processor. The count of scheduled nodes in this scheduler
* instance equals the processor count owned by the scheduler instance.
*/
SCHEDULER_SMP_NODE_SCHEDULED,
/**
* @brief This scheduler node is ready.
*
* A scheduler node is ready if the corresponding thread is ready and the
* scheduler did not allocate a processor for it.
*/
SCHEDULER_SMP_NODE_READY
} Scheduler_SMP_Node_state;
--
Sebastian Huber, embedded brains GmbH
Address : Dornierstr. 4, D-82178 Puchheim, Germany
Phone : +49 89 189 47 41-16
Fax : +49 89 189 47 41-09
E-Mail : sebastian.hu...@embedded-brains.de
PGP : Public key available on request.
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