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incubator-nuttx/sched/paging/pg_worker.c

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/****************************************************************************
* sched/paging/pg_worker.c
*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership. The
* ASF licenses this file to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance with the
* License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations
* under the License.
*
****************************************************************************/
/****************************************************************************
* Included Files
****************************************************************************/
#include <nuttx/config.h>
#include <stdint.h>
#include <stdbool.h>
#include <unistd.h>
#include <assert.h>
#include <errno.h>
#include <debug.h>
#include <nuttx/queue.h>
#include <nuttx/sched.h>
#include <nuttx/arch.h>
#include <nuttx/signal.h>
#include <nuttx/page.h>
#include <nuttx/clock.h>
#include <nuttx/signal.h>
#include "sched/sched.h"
#include "paging/paging.h"
#ifdef CONFIG_PAGING
/****************************************************************************
* Public Data
****************************************************************************/
/* This is the task ID of the page fill worker thread. This value was set in
* nx_start when the page fill worker thread was started.
*/
pid_t g_pgworker;
/* The page fill worker thread maintains a static variable called g_pftcb.
* If no fill is in progress, g_pftcb will be NULL. Otherwise, g_pftcb will
* point to the TCB of the task which is receiving the fill that is in
* progress.
*
* NOTE: I think that this is the only state in which a TCB does not reside
* in some list. Here is it in limbo, outside of the normally queuing while
* the page file is in progress. Where here, it will be marked with
* TSTATE_TASK_INVALID.
*/
FAR struct tcb_s *g_pftcb;
/****************************************************************************
* Private Data
****************************************************************************/
#ifndef CONFIG_PAGING_BLOCKINGFILL
/* When a page fill completes, the result of the fill is stored here. The
* value -EBUSY means that the page fill callback has not yet been received.
*/
static int g_fillresult;
/* A configurable timeout period (in clock ticks) may be select to detect
* page fill failures.
*/
#ifdef CONFIG_PAGING_TIMEOUT_TICKS
static clock_t g_starttime;
#endif
#endif
/****************************************************************************
* Private Functions
****************************************************************************/
/****************************************************************************
* Name: pg_callback
*
* Description:
* This function is called from the architecture-specific, page fill logic
* when the page fill completes (with or without an error). A reference to
* this function was provided to up_fillpage(). The driver will provide
* the result of the fill as an argument.
*
* NOTE: pg_callback() must also be locked in memory.
*
* When pg_callback() is called, it will perform the following operations:
*
* - Verify that g_pftcb is non-NULL.
* - Find the higher priority between the task waiting for the fill to
* complete in g_pftcb and the task waiting at the head of the
* g_waitingforfill list. That will be the priority of he highest priority
* task waiting for a fill.
* - If this higher priority is higher than current page fill worker thread,
* then boost worker thread's priority to that level. Thus, the page fill
* worker thread will always run at the priority of the highest priority
* task that is waiting for a fill.
* - Signal the page fill worker thread.
*
* Input Parameters:
* tcb - The TCB of the task that just received the fill.
* result - The result of the page fill operation.
*
* Returned Value:
* None
*
* Assumptions:
* Possibly executing in the context of a driver interrupt handler???
*
****************************************************************************/
#ifndef CONFIG_PAGING_BLOCKINGFILL
static void pg_callback(FAR struct tcb_s *tcb, int result)
{
/* Verify that g_pftcb is non-NULL */
pginfo("g_pftcb: %p\n", g_pftcb);
if (g_pftcb)
{
FAR struct tcb_s *htcb = (FAR struct tcb_s *)g_waitingforfill.head;
FAR struct tcb_s *wtcb = nxsched_get_tcb(g_pgworker);
/* Find the higher priority between the task waiting for the fill to
* complete in g_pftcb and the task waiting at the head of the
* g_waitingforfill list. That will be the priority of he highest
* priority task waiting for a fill.
*/
int priority = g_pftcb->sched_priority;
if (htcb && priority < htcb->sched_priority)
{
priority = htcb->sched_priority;
}
/* If this higher priority is higher than current page fill worker
* thread, then boost worker thread's priority to that level. Thus,
* the page fill worker thread will always run at the priority of
* the highest priority task that is waiting for a fill.
*/
if (priority > wtcb->sched_priority)
{
pginfo("New worker priority. %d->%d\n",
wtcb->sched_priority, priority);
nxsched_set_priority(wtcb, priority);
}
/* Save the page fill result (don't permit the value -EBUSY) */
if (result == -EBUSY)
{
result = -ENOSYS;
}
g_fillresult = result;
}
/* Signal the page fill worker thread (in any event) */
pginfo("Signaling worker. PID: %d\n", g_pgworker);
nxsig_kill(g_pgworker, SIGPAGING);
}
#endif
/****************************************************************************
* Name: pg_dequeue
*
* Description:
* Dequeue the next, highest priority TCB from the g_waitingforfill task
* list. Call up_checkmapping() see if the still needs to be performed
* for that task. In certain conditions, the page fault may occur on
* several threads for the same page and be queued multiple times. In this
* corner case, the blocked task will simply be restarted.
*
* This function will continue to examine g_waitingforfill until either
* (1) a task is found that still needs the page fill, or (2) the
* g_waitingforfill task list becomes empty.
*
* The result (NULL or a TCB pointer) will be returned in the global
* variable, g_pftcb.
*
* Input Parameters:
* None
*
* Returned Value:
* If there are no further queue page fill operations to be performed,
* pg_dequeue() will return false. Otherwise, it will return
* true to that the full is in process (any errors will result in
* assertions and this function will not return).
*
* Assumptions:
* Executing in the context of the page fill worker thread with all
* interrupts disabled.
*
****************************************************************************/
static inline bool pg_dequeue(void)
{
FAR struct tcb_s *wtcb = this_task();
/* Loop until either (1) the TCB of a task that requires a fill is found,
* OR (2) the g_watingforfill list becomes empty.
*/
do
{
/* Remove the TCB from the head of the list (if any) */
g_pftcb = (FAR struct tcb_s *)dq_remfirst(&g_waitingforfill);
pginfo("g_pftcb: %p\n", g_pftcb);
if (g_pftcb != NULL)
{
/* Call the architecture-specific function up_checkmapping() to see
* if the page fill still needs to be performed. In certain
* conditions, the page fault may occur on several threads for the
* same page and be queues multiple times. In this corner case, the
* blocked task will simply be restarted.
*/
if (!up_checkmapping(g_pftcb))
{
/* This page needs to be filled. pg_miss bumps up
* the priority of the page fill worker thread as each
* TCB is added to the g_waitingforfill list. So we
* may need to also drop the priority of the worker
* thread as the next TCB comes off of the list.
*
* If wtcb->sched_priority > CONFIG_PAGING_DEFPRIO,
* then the page fill worker thread is executing at
* an elevated priority that may be reduced.
*
* If wtcb->sched_priority > g_pftcb->sched_priority
* then the page fill worker thread is executing at
* a higher priority than is appropriate for this
* fill (this priority can get re-boosted by pg_miss()
* if a new higher priority fill is required).
*/
if (wtcb->sched_priority > CONFIG_PAGING_DEFPRIO &&
wtcb->sched_priority > g_pftcb->sched_priority)
{
/* Don't reduce the priority of the page fill
* worker thread lower than the configured
* minimum.
*/
int priority = g_pftcb->sched_priority;
if (priority < CONFIG_PAGING_DEFPRIO)
{
priority = CONFIG_PAGING_DEFPRIO;
}
/* Reduce the priority of the page fill worker thread */
pginfo("New worker priority. %d->%d\n",
wtcb->sched_priority, priority);
nxsched_set_priority(wtcb, priority);
}
/* Return with g_pftcb holding the pointer to
* the TCB associated with task that requires the page fill.
*/
return true;
}
/* The page need by this task has already been mapped into the
* virtual address space -- just restart it.
*/
pginfo("Restarting TCB: %p\n", g_pftcb);
/* Add the task to ready-to-run task list and
* perform the context switch if one is needed
*/
if (nxsched_add_readytorun(g_pftcb))
{
up_switch_context(g_pftcb, wtcb);
}
}
}
while (g_pftcb != NULL);
return false;
}
/****************************************************************************
* Name: pg_startfill
*
* Description:
* Start a page fill operation on the thread whose TCB is at the head of
* of the g_waitingforfill task list. That is a prioritized list so that
* will be the highest priority task waiting for a page fill (in the event
* that are multiple tasks waiting for a page fill).
*
* This function may be called either (1) when the page fill worker thread
* is notified that there is a new page fill TCB in the g_waitingforfill
* prioritized list, or (2) when a page fill completes and there are more
* pages to be filled in g_waitingforfill list.
*
* Input Parameters:
* None
*
* Returned Value:
* If there are no further queue page fill operations to be performed,
* pg_startfill() will return false. Otherwise, it will return
* true to that the full is in process (any errors will result in
* assertions and this function will not return).
*
* Assumptions:
* Executing in the context of the page fill worker thread with all
* interrupts disabled.
*
****************************************************************************/
static inline bool pg_startfill(void)
{
FAR void *vpage;
int result;
/* Remove the TCB at the head of the g_waitfor fill list and check if there
* is any task waiting for a page fill. pg_dequeue will handle this (plus
* some corner cases) and will true if the next page TCB was successfully
* dequeued.
*/
if (pg_dequeue())
{
/* Call up_allocpage(tcb, &vpage). This architecture-specific function
* will set aside page in memory and map to virtual address (vpage). If
* all available pages are in-use (the typical case), this function
* will select a page in-use, un-map it, and make it available.
*/
pginfo("Call up_allocpage(%p)\n", g_pftcb);
result = up_allocpage(g_pftcb, &vpage);
DEBUGASSERT(result == OK);
/* Start the fill. The exact way that the fill is started depends upon
* the nature of the architecture-specific up_fillpage() function -- Is
* it a blocking or a non-blocking call?
*/
#ifdef CONFIG_PAGING_BLOCKINGFILL
/* If CONFIG_PAGING_BLOCKINGFILL is defined, then up_fillpage is
* blocking call. In this case, up_fillpage() will accept only (1) a
* reference to the TCB that requires the fill. Architecture-specific
* context information within the TCB will be sufficient to perform the
* fill. And (2) the (virtual) address of the allocated page to be
* filled. The resulting status of the fill will be provided by return
* value from up_fillpage().
*/
pginfo("Call up_fillpage(%p)\n", g_pftcb);
result = up_fillpage(g_pftcb, vpage);
DEBUGASSERT(result == OK);
#else
/* If CONFIG_PAGING_BLOCKINGFILL is defined, then up_fillpage is non-
* blocking call. In this case up_fillpage() will accept an additional
* argument: The page fill worker thread will provide a callback
* function, pg_callback.
* up_fillpage will start an asynchronous page fill. pg_callback
* will be called when the page fill is finished (or an error occurs).
* This callback will probably from interrupt level.
*/
pginfo("Call up_fillpage(%p)\n", g_pftcb);
result = up_fillpage(g_pftcb, vpage, pg_callback);
DEBUGASSERT(result == OK);
/* Save the time that the fill was started. These will be used to
* check for timeouts.
*/
#ifdef CONFIG_PAGING_TIMEOUT_TICKS
g_starttime = clock_systime_ticks();
#endif
/* Return and wait to be signaled for the next event -- the fill
* completion event. While the fill is in progress, other tasks may
* execute. If another page fault occurs during this time, the faulting
* task will be blocked, its TCB will be added (in priority order) to
* g_waitingforfill and the priority of the page worker task may be
* boosted. But no action will be taken until the current page fill
* completes. NOTE: The IDLE task must also be fully locked in memory.
* The IDLE task cannot be blocked. It the case where all tasks are
* blocked waiting for a page fill, the IDLE task must still be
* available to run.
*/
#endif /* CONFIG_PAGING_BLOCKINGFILL */
return true;
}
pginfo("Queue empty\n");
UNUSED(result);
return false;
}
/****************************************************************************
* Name: pg_alldone
*
* Description:
* Called by the page fill worker thread when all pending page fill
* operations have been completed and the g_waitingforfill list is empty.
*
* This function will perform the following operations:
*
* - Set g_pftcb to NULL.
* - Restore the default priority of the page fill worker thread.
*
* Input Parameters:
* None.
*
* Returned Value:
* None
*
* Assumptions:
* Executing in the context of the page fill worker thread with interrupts
* disabled.
*
****************************************************************************/
static inline void pg_alldone(void)
{
FAR struct tcb_s *wtcb = this_task();
g_pftcb = NULL;
pginfo("New worker priority. %d->%d\n",
wtcb->sched_priority, CONFIG_PAGING_DEFPRIO);
nxsched_set_priority(wtcb, CONFIG_PAGING_DEFPRIO);
}
/****************************************************************************
* Name: pg_fillcomplete
*
* Description:
* Called by the page fill worker thread when a page fill completes.
* Either (1) in the non-blocking up_fillpage(), after the architecture-
* specific driver call the pg_callback() to wake up the page fill worker
* thread, or (2) after the blocking up_fillpage() returns (when
* CONFIG_PAGING_BLOCKINGFILL is defined).
*
* This function is just a dumb wrapper around up_unblocktask(). This
* function simply makes the task that just received the fill ready-to-run.
*
* Input Parameters:
* None.
*
* Returned Value:
* None
*
* Assumptions:
* Executing in the context of the page fill worker thread with interrupts
* disabled.
*
****************************************************************************/
static inline void pg_fillcomplete(void)
{
FAR struct tcb_s *wtcb = this_task();
/* Call up_unblocktask(g_pftcb) to make the task that just
* received the fill ready-to-run.
*/
pginfo("Restarting TCB: %p\n", g_pftcb);
/* Add the task to ready-to-run task list and
* perform the context switch if one is needed
*/
if (nxsched_add_readytorun(g_pftcb))
{
up_switch_context(g_pftcb, wtcb);
}
}
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Name: pg_worker
*
* Description:
* This is the page fill worker thread that performs pages fills for tasks
* that have received a pag fault and are blocked in the g_waitingforfill
* task queue.
*
* The page fill worker thread will be awakened on one of three conditions:
* - When signaled by pg_miss(), the page fill worker thread will be
* awakened, or
* - if CONFIG_PAGING_BLOCKINGFILL is not defined, from pg_callback()
* after completing a page fill.
* - A configurable timeout with no activity.
*
* Input Parameters:
* argc, argv (not used)
*
* Returned Value:
* Does not return
*
****************************************************************************/
int pg_worker(int argc, FAR char *argv[])
{
FAR struct tcb_s *wtcb = this_task();
/* Loop forever -- Notice that interrupts will be disabled at all times
* that this thread runs. That is so that we can't lose signals or have
* asynchronous page faults.
*
* All interrupt logic as well as all page fill worker thread logic must
* be locked in memory. Therefore, keeping interrupts disabled here
* should prevent any concurrent page faults. Any page faults or page
* fill completions should occur while this thread sleeps.
*/
pginfo("Started\n");
up_irq_save();
for (; ; )
{
/* Wait awhile. We will wait here until either the configurable
* timeout elapses or until we are awakened by a signal (which
* terminates the nxsig_usleep with an EINTR error). Note that
* interrupts will be re- enabled while this task sleeps.
*
* The timeout is a failsafe that will handle any cases where a single
* is lost (that would really be a bug and shouldn't happen!) and also
* supports timeouts for case of non-blocking, asynchronous fills.
*/
nxsig_usleep(CONFIG_PAGING_WORKPERIOD);
/* The page fill worker thread will be awakened on one of 3 conditions:
*
* - When signaled by pg_miss(), the page fill worker thread will be
* awakened,
* - if CONFIG_PAGING_BLOCKINGFILL is not defined, from pg_callback()
* after completing a page fill, or
* - On a configurable timeout expires with no activity.
*
* Interrupts are still disabled.
*/
#ifndef CONFIG_PAGING_BLOCKINGFILL
/* For the non-blocking up_fillpage(), the page fill worker thread will
* detect that the page fill is complete when it is awakened with
* g_pftcb non-NULL and fill completion status from pg_callback.
*/
if (g_pftcb != NULL)
{
/* If it is a real page fill completion event, then the result of
* the page fill will be in g_fillresult and will not be equal to
* -EBUSY.
*/
if (g_fillresult != -EBUSY)
{
/* Any value other than OK, brings the system down */
DEBUGASSERT(g_fillresult == OK);
/* Handle the successful page fill complete event by restarting
* the task that was blocked waiting for this page fill.
*/
pginfo("Restarting TCB: %p\n", g_pftcb);
/* Add the task to ready-to-run task list and
* perform the context switch if one is needed
*/
if (nxsched_add_readytorun(g_pftcb))
{
up_switch_context(g_pftcb, wtcb);
}
/* Yes .. Start the next asynchronous fill. Check the return
* value to see a fill was actually started (false means that
* no fill was started).
*/
pginfo("Calling pg_startfill\n");
if (!pg_startfill())
{
/* No fill was started. This can mean only that all queued
* page fill actions have and been completed and there is
* nothing more to do.
*/
pginfo("Call pg_alldone()\n");
pg_alldone();
}
}
/* If a configurable timeout period expires with no page fill
* completion event, then declare a failure.
*/
#ifdef CONFIG_PAGING_TIMEOUT_TICKS
else
{
pgerr("ERROR: Timeout!\n");
DEBUGASSERT(clock_systime_ticks() - g_starttime <
CONFIG_PAGING_TIMEOUT_TICKS);
}
#endif
}
/* Otherwise, this might be a page fill initiation event. When
* awakened from pg_miss(), no fill will be in progress and
* g_pftcb will be NULL.
*/
else
{
/* Are there tasks blocked and waiting for a fill? If so,
* pg_startfill() will start the asynchronous fill (and set
* g_pftcb).
*/
pginfo("Calling pg_startfill\n");
pg_startfill();
}
#else
/* Are there tasks blocked and waiting for a fill? Loop until all
* pending fills have been processed.
*/
for (; ; )
{
/* Yes .. Start the fill and block until the fill completes.
* Check the return value to see a fill was actually performed.
* (false means that no fill was performed).
*/
pginfo("Calling pg_startfill\n");
if (!pg_startfill())
{
/* Break out of the loop -- there is nothing more to do */
break;
}
/* Handle the page fill complete event by restarting the
* task that was blocked waiting for this page fill. In the
* non-blocking fill case, the page fill worker thread will
* know that the page fill is complete when pg_startfill()
* returns true.
*/
pginfo("Restarting TCB: %p\n", g_pftcb);
/* Add the task to ready-to-run task list and
* perform the context switch if one is needed
*/
if (nxsched_add_readytorun(g_pftcb))
{
up_switch_context(g_pftcb, wtcb);
}
}
/* All queued fills have been processed */
pginfo("Call pg_alldone()\n");
pg_alldone();
#endif
}
return OK; /* To keep some compilers happy */
}
#endif /* CONFIG_PAGING */
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