nuttx/sched/wqueue/kwork_queue.c
Zhe Weng c9a38f42f7 sched/wqueue: Do as much work as possible in work_thread
Decouple the semcount and the work queue length.

Previous Problem:

If a work is queued and cancelled in high priority threads (or queued
by timer and cancelled by another high priority thread) before
work_thread runs, the queue operation will mark work_thread as ready to
run, but the cancel operation minus the semcount back to -1 and makes
wqueue->q empty. Then the work_thread still runs, found empty queue,
and wait sem again, then semcount becomes -2 (being minused by 1)

This can be done multiple times, then semcount can become very small
value. Test case to produce incorrect semcount:

high_priority_task()
{
  for (int i = 0; i < 10000; i++)
    {
      work_queue(LPWORK, &work, worker, NULL, 0);
      work_cancel(LPWORK, &work);
      usleep(1);
    }

  /* Now the g_lpwork.sem.semcount is a value near -10000 */
}

With incorrect semcount, any queue operation when the work_thread is
busy, will only increase semcount and push work into queue, but cannot
trigger work_thread (semcount is negative but work_thread is not
waiting), then there will be more and more works left in queue while
the work_thread is waiting sem and cannot call them.

Signed-off-by: Zhe Weng <wengzhe@xiaomi.com>
2023-03-21 17:50:40 +02:00

192 lines
5.7 KiB
C

/****************************************************************************
* sched/wqueue/kwork_queue.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 <assert.h>
#include <errno.h>
#include <nuttx/irq.h>
#include <nuttx/arch.h>
#include <nuttx/clock.h>
#include <nuttx/queue.h>
#include <nuttx/wqueue.h>
#include "wqueue/wqueue.h"
#ifdef CONFIG_SCHED_WORKQUEUE
/****************************************************************************
* Pre-processor Definitions
****************************************************************************/
#define queue_work(wqueue, work) \
do \
{ \
int sem_count; \
dq_addlast((FAR dq_entry_t *)(work), &(wqueue).q); \
nxsem_get_value(&(wqueue).sem, &sem_count); \
if (sem_count < 0) /* There are threads waiting for sem. */ \
{ \
nxsem_post(&(wqueue).sem); \
} \
} \
while (0)
/****************************************************************************
* Private Functions
****************************************************************************/
/****************************************************************************
* Name: hp_work_timer_expiry
****************************************************************************/
#ifdef CONFIG_SCHED_HPWORK
static void hp_work_timer_expiry(wdparm_t arg)
{
irqstate_t flags = enter_critical_section();
queue_work(g_hpwork, arg);
leave_critical_section(flags);
}
#endif
/****************************************************************************
* Name: lp_work_timer_expiry
****************************************************************************/
#ifdef CONFIG_SCHED_LPWORK
static void lp_work_timer_expiry(wdparm_t arg)
{
irqstate_t flags = enter_critical_section();
queue_work(g_lpwork, arg);
leave_critical_section(flags);
}
#endif
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Name: work_queue
*
* Description:
* Queue kernel-mode work to be performed at a later time. All queued
* work will be performed on the worker thread of execution (not the
* caller's).
*
* The work structure is allocated and must be initialized to all zero by
* the caller. Otherwise, the work structure is completely managed by the
* work queue logic. The caller should never modify the contents of the
* work queue structure directly. If work_queue() is called before the
* previous work has been performed and removed from the queue, then any
* pending work will be canceled and lost.
*
* Input Parameters:
* qid - The work queue ID (index)
* work - The work structure to queue
* worker - The worker callback to be invoked. The callback will be
* invoked on the worker thread of execution.
* arg - The argument that will be passed to the worker callback when
* int is invoked.
* delay - Delay (in clock ticks) from the time queue until the worker
* is invoked. Zero means to perform the work immediately.
*
* Returned Value:
* Zero on success, a negated errno on failure
*
****************************************************************************/
int work_queue(int qid, FAR struct work_s *work, worker_t worker,
FAR void *arg, clock_t delay)
{
irqstate_t flags;
int ret = OK;
/* Interrupts are disabled so that this logic can be called from with
* task logic or from interrupt handling logic.
*/
flags = enter_critical_section();
/* Remove the entry from the timer and work queue. */
if (work->worker != NULL)
{
work_cancel(qid, work);
}
/* Initialize the work structure. */
work->worker = worker; /* Work callback. non-NULL means queued */
work->arg = arg; /* Callback argument */
/* Queue the new work */
#ifdef CONFIG_SCHED_HPWORK
if (qid == HPWORK)
{
/* Queue high priority work */
if (!delay)
{
queue_work(g_hpwork, work);
}
else
{
wd_start(&work->u.timer, delay, hp_work_timer_expiry,
(wdparm_t)work);
}
}
else
#endif
#ifdef CONFIG_SCHED_LPWORK
if (qid == LPWORK)
{
/* Queue low priority work */
if (!delay)
{
queue_work(g_lpwork, work);
}
else
{
wd_start(&work->u.timer, delay, lp_work_timer_expiry,
(wdparm_t)work);
}
}
else
#endif
{
ret = -EINVAL;
}
leave_critical_section(flags);
return ret;
}
#endif /* CONFIG_SCHED_WORKQUEUE */