Squashed commit of the following:

fs/procfs/fs_procfsproc:  Extended the process ID ProcFS output to show per-thread maximum time for pre-emption disabled and maximum time within a critical section.

    sched/sched/sched_critmonitor.c:  Adds data collection logic in support of monitoring critical sections and pre-emption state.

fs/procfs/fs_procfsproc.c

@@ -53,6 +53,10 @@
 #include <errno.h>
 #include <debug.h>
 
+#ifdef CONFIG_SCHED_CRITMONITOR
+#  include <time.h>
+#endif
+
 #include <nuttx/irq.h>
 #include <nuttx/arch.h>
 #include <nuttx/sched.h>
@@ -62,7 +66,7 @@
 #include <nuttx/fs/procfs.h>
 #include <nuttx/fs/dirent.h>
 
-#ifdef CONFIG_SCHED_CPULOAD
+#if defined(CONFIG_SCHED_CPULOAD) || defined(CONFIG_SCHED_CRITMONITOR)
 #  include <nuttx/clock.h>
 #endif
 
@@ -105,6 +109,9 @@ enum proc_node_e
   PROC_CMDLINE,                       /* Task command line */
 #ifdef CONFIG_SCHED_CPULOAD
   PROC_LOADAVG,                       /* Average CPU utilization */
+#endif
+#ifdef CONFIG_SCHED_CRITMONITOR
+  PROC_CRITMON,                       /* Critical section monitor */
 #endif
   PROC_STACK,                         /* Task stack info */
   PROC_GROUP,                         /* Group directory */
@@ -167,9 +174,24 @@ static FAR const char *g_policy[4] =
   "SCHED_FIFO", "SCHED_RR", "SCHED_SPORADIC", "SCHED_OTHER"
 };
 
+/****************************************************************************
+ * External Function Prototypes
+ ****************************************************************************/
+
+#ifdef CONFIG_SCHED_CRITMONITOR
+/* If CONFIG_SCHED_CRITMONITOR is selected, then platform-specific logic
+ * must provide the following interface.  This interface simply converts an
+ * elapsed time into well known units for presentation by the ProcFS file
+ * system..
+ */
+
+void up_critmon_convert(uint32_t starttime, FAR struct timespec *ts);
+#endif
+
 /****************************************************************************
  * Private Function Prototypes
  ****************************************************************************/
+
 /* Helpers */
 
 static FAR const struct proc_node_s *
@@ -185,6 +207,11 @@ static ssize_t proc_loadavg(FAR struct proc_file_s *procfile,
                  FAR struct tcb_s *tcb, FAR char *buffer, size_t buflen,
                  off_t offset);
 #endif
+#ifdef CONFIG_SCHED_CRITMONITOR
+static ssize_t proc_critmon(FAR struct proc_file_s *procfile,
+                 FAR struct tcb_s *tcb, FAR char *buffer, size_t buflen,
+                 off_t offset);
+#endif
 static ssize_t proc_stack(FAR struct proc_file_s *procfile,
                  FAR struct tcb_s *tcb, FAR char *buffer, size_t buflen,
                  off_t offset);
@@ -273,6 +300,13 @@ static const struct proc_node_s g_loadavg =
 };
 #endif
 
+#ifdef CONFIG_SCHED_CRITMONITOR
+static const struct proc_node_s g_critmon =
+{
+  "critmon",       "critmon", (uint8_t)PROC_CRITMON,     DTYPE_FILE        /* Critical Section Monitor */
+};
+#endif
+
 static const struct proc_node_s g_stack =
 {
   "stack",        "stack",   (uint8_t)PROC_STACK,        DTYPE_FILE        /* Task stack info */
@@ -309,6 +343,9 @@ static FAR const struct proc_node_s * const g_nodeinfo[] =
   &g_cmdline,      /* Task command line */
 #ifdef CONFIG_SCHED_CPULOAD
   &g_loadavg,      /* Average CPU utilization */
+#endif
+#ifdef CONFIG_SCHED_CRITMONITOR
+  &g_critmon,      /* Critical section Monitor */
 #endif
   &g_stack,        /* Task stack info */
   &g_group,        /* Group directory */
@@ -329,6 +366,9 @@ static const struct proc_node_s * const g_level0info[] =
   &g_cmdline,      /* Task command line */
 #ifdef CONFIG_SCHED_CPULOAD
   &g_loadavg,      /* Average CPU utilization */
+#endif
+#ifdef CONFIG_SCHED_CRITMONITOR
+  &g_critmon,      /* Critical section monitor */
 #endif
   &g_stack,        /* Task stack info */
   &g_group,        /* Group directory */
@@ -743,6 +783,84 @@ static ssize_t proc_loadavg(FAR struct proc_file_s *procfile,
 }
 #endif
 
+/****************************************************************************
+ * Name: proc_critmon
+ ****************************************************************************/
+
+#ifdef CONFIG_SCHED_CRITMONITOR
+static ssize_t proc_critmon(FAR struct proc_file_s *procfile,
+                            FAR struct tcb_s *tcb, FAR char *buffer,
+                            size_t buflen, off_t offset)
+{
+  struct timespec maxtime;
+  size_t remaining;
+  size_t linesize;
+  size_t copysize;
+  size_t totalsize;
+
+  remaining = buflen;
+  totalsize = 0;
+
+  /* Convert the for maximum time pre-emption disabled */
+
+  if (tcb->premp_max > 0)
+    {
+      up_critmon_convert(tcb->premp_max, &maxtime);
+    }
+  else
+    {
+      maxtime.tv_sec = 0;
+      maxtime.tv_nsec = 0;
+    }
+
+  /* Reset the maximum */
+
+  tcb->premp_max = 0;
+
+  /* Generate output for maximum time pre-emption disabled */
+
+  linesize = snprintf(procfile->line, STATUS_LINELEN, "%lu.%09lu,",
+                     (unsigned long)maxtime.tv_sec,
+                     (unsigned long)maxtime.tv_nsec);
+  copysize = procfs_memcpy(procfile->line, linesize, buffer, buflen, &offset);
+
+  totalsize += copysize;
+  buffer    += copysize;
+  remaining -= copysize;
+
+  if (totalsize >= buflen)
+    {
+      return totalsize;
+    }
+
+  /* Convert and generate output for maximum time in a critical section */
+
+  if (tcb->crit_max > 0)
+    {
+      up_critmon_convert(tcb->crit_max, &maxtime);
+    }
+  else
+    {
+      maxtime.tv_sec = 0;
+      maxtime.tv_nsec = 0;
+    }
+
+  /* Reset the maximum */
+
+  tcb->crit_max = 0;
+
+  /* Generate output for maximum time in a critical section */
+
+  linesize = snprintf(procfile->line, STATUS_LINELEN, "%lu.%09lu\n",
+                     (unsigned long)maxtime.tv_sec,
+                     (unsigned long)maxtime.tv_nsec);
+  copysize = procfs_memcpy(procfile->line, linesize, buffer, buflen, &offset);
+
+  totalsize += copysize;
+  return totalsize;
+}
+#endif
+
 /****************************************************************************
  * Name: proc_stack
  ****************************************************************************/
@@ -1324,6 +1442,11 @@ static ssize_t proc_read(FAR struct file *filep, FAR char *buffer,
     case PROC_LOADAVG: /* Average CPU utilization */
       ret = proc_loadavg(procfile, tcb, buffer, buflen, filep->f_pos);
       break;
+#endif
+#ifdef CONFIG_SCHED_CRITMONITOR
+    case PROC_CRITMON: /* Critical section monitor */
+      ret = proc_critmon(procfile, tcb, buffer, buflen, filep->f_pos);
+      break;
 #endif
     case PROC_STACK: /* Task stack info */
       ret = proc_stack(procfile, tcb, buffer, buflen, filep->f_pos);

include/nuttx/irq.h

@@ -1,7 +1,8 @@
 /****************************************************************************
  * include/nuttx/irq.h
  *
- *   Copyright (C) 2007-2011, 2013, 2016-2017 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2007-2011, 2013, 2016-2017 Gregory Nutt. All rights
+ *     reserved.
  *   Author: Gregory Nutt <gnutt@nuttx.org>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -196,7 +197,8 @@ int irqchain_detach(int irq, xcpt_t isr, FAR void *arg);
  *
  ****************************************************************************/
 
-#if defined(CONFIG_SMP) || defined(CONFIG_SCHED_INSTRUMENTATION_CSECTION)
+#if defined(CONFIG_SMP) || defined(CONFIG_SCHED_INSTRUMENTATION_CSECTION) || \
+    defined(CONFIG_SCHED_CRITMONITOR)
 irqstate_t enter_critical_section(void);
 #else
 #  define enter_critical_section(f) up_irq_save(f)
@@ -223,7 +225,8 @@ irqstate_t enter_critical_section(void);
  *
  ****************************************************************************/
 
-#if defined(CONFIG_SMP) || defined(CONFIG_SCHED_INSTRUMENTATION_CSECTION)
+#if defined(CONFIG_SMP) || defined(CONFIG_SCHED_INSTRUMENTATION_CSECTION) || \
+    defined(CONFIG_SCHED_CRITMONITOR)
 void leave_critical_section(irqstate_t flags);
 #else
 #  define leave_critical_section(f) up_irq_restore(f)

include/nuttx/sched.h

@@ -696,6 +696,16 @@ struct tcb_s
   FAR void *pthread_data[CONFIG_NPTHREAD_KEYS];
 #endif
 
+  /* Pre-emption monitor support ************************************************/
+
+#ifdef CONFIG_SCHED_CRITMONITOR
+  uint32_t crit_flags;                   /* Flag values used by the monitor     */
+  uint32_t premp_start;                  /* Time when preemption disabled       */
+  uint32_t premp_max;                    /* Max time preemption disabled        */
+  uint32_t crit_start;                   /* Time critical section entered       */
+  uint32_t crit_max;                     /* Max time in critical section        */
+#endif
+
   /* Library related fields *****************************************************/
 
   int pterrno;                           /* Current per-thread errno            */
@@ -931,7 +941,8 @@ int group_exitinfo(pid_t pid, FAR struct binary_s *bininfo);
  ********************************************************************************/
 
 #if CONFIG_RR_INTERVAL > 0 || defined(CONFIG_SCHED_SPORADIC) || \
-    defined(CONFIG_SCHED_INSTRUMENTATION) || defined(CONFIG_SMP)
+    defined(CONFIG_SCHED_INSTRUMENTATION) || defined(CONFIG_SCHED_CRITMONITOR) || \
+    defined(CONFIG_SMP)
 void sched_resume_scheduler(FAR struct tcb_s *tcb);
 #else
 #  define sched_resume_scheduler(tcb)
@@ -953,7 +964,8 @@ void sched_resume_scheduler(FAR struct tcb_s *tcb);
  *
  ********************************************************************************/
 
-#if defined(CONFIG_SCHED_SPORADIC) || defined(CONFIG_SCHED_INSTRUMENTATION)
+#if defined(CONFIG_SCHED_SPORADIC) || defined(CONFIG_SCHED_INSTRUMENTATION) || \
+    defined(CONFIG_SCHED_CRITMONITOR)
 void sched_suspend_scheduler(FAR struct tcb_s *tcb);
 #else
 #  define sched_suspend_scheduler(tcb)

sched/Kconfig

@@ -700,6 +700,39 @@ config SCHED_IRQMONITOR
 		counts will be available in the mounted procfs file systems at the
 		top-level file, "irqs".
 
+config SCHED_CRITMONITOR
+	bool "Enable Critical Section monitoring"
+	default n
+	depends on FS_PROCFS
+	---help---
+		Enables logic that monitors the duration of time that a thread keeps
+		interrupts or pre-emption disabled.  These global locks can have
+		negative consequences to real timer performance:  Disabling interrupts
+		adds jitter in the time when a interrupt request is asserted until
+		the hardware can responds with the interrupt.  Disabling pre-emption
+		adds jitter in the timer from when the event is posted in the
+		interrupt handler until the task that responds to the event can run.
+
+		If this option is selected, then the following interfaces must be
+		provided by platform-specific logic:
+
+			uint32_t up_critmon_gettime(void);
+			void up_critmon_convert(uint32_t starttime, FAR struct timespec *ts);
+
+		The first interface simply provides the current time value in unknown
+		units.  NOTE:  This function may be called early before the timer has
+		been initialized.  In that event, the function should just return a
+		start time of zero.
+
+		Nothing is assumed about the units of this time value.  The following
+		are assumed, however: (1) The time is an unsigned is an unsigned integer
+		value, (2) is is monotonically increasing, and (3) the elapsed time
+		(also in unknown units) can be obtained by subtracting a start time
+		from the current time.
+
+		The second interface simple converts an elapsed time into well known
+		units for presentation by the ProcFS file system..
+
 config SCHED_CPULOAD
 	bool "Enable CPU load monitoring"
 	default n

sched/irq/Make.defs

@@ -44,6 +44,8 @@ endif
 endif
 else ifeq ($(CONFIG_SCHED_INSTRUMENTATION_CSECTION),y)
 CSRCS += irq_csection.c
+else ifeq ($(CONFIG_SCHED_CRITMONITOR),y)
+CSRCS += irq_csection.c
 endif
 
 ifeq ($(CONFIG_SCHED_IRQMONITOR),y)

sched/irq/irq_csection.c

@@ -49,7 +49,8 @@
 #include "sched/sched.h"
 #include "irq/irq.h"
 
-#if defined(CONFIG_SMP) || defined(CONFIG_SCHED_INSTRUMENTATION_CSECTION)
+#if defined(CONFIG_SMP) || defined(CONFIG_SCHED_INSTRUMENTATION_CSECTION) || \
+    defined(CONFIG_SCHED_CRITMONITOR)
 
 /****************************************************************************
  * Public Data
@@ -375,9 +376,12 @@ try_again:
                           &g_cpu_irqlock);
               rtcb->irqcount = 1;
 
-#ifdef CONFIG_SCHED_INSTRUMENTATION_CSECTION
               /* Note that we have entered the critical section */
 
+#ifdef CONFIG_SCHED_CRITMONITOR
+              sched_critmon_csection(rtcb, true);
+#endif
+#ifdef CONFIG_SCHED_INSTRUMENTATION_CSECTION
               sched_note_csection(rtcb, true);
 #endif
             }
@@ -388,7 +392,8 @@ try_again:
 
   return ret;
 }
-#else /* defined(CONFIG_SCHED_INSTRUMENTATION_CSECTION) */
+#else /* defined(CONFIG_SCHED_INSTRUMENTATION_CSECTION) || \
+       * defined(CONFIG_SCHED_CRITMONITOR) */
 irqstate_t enter_critical_section(void)
 {
   irqstate_t ret;
@@ -408,7 +413,12 @@ irqstate_t enter_critical_section(void)
 
       /* Yes.. Note that we have entered the critical section */
 
+#ifdef CONFIG_SCHED_CRITMONITOR
+      sched_critmon_csection(rtcb, true);
+#endif
+#ifdef CONFIG_SCHED_INSTRUMENTATION_CSECTION
       sched_note_csection(rtcb, true);
+#endif
     }
 
   /* Return interrupt status */
@@ -507,9 +517,12 @@ void leave_critical_section(irqstate_t flags)
             }
           else
             {
-#ifdef CONFIG_SCHED_INSTRUMENTATION_CSECTION
               /* No.. Note that we have left the critical section */
 
+#ifdef CONFIG_SCHED_CRITMONITOR
+              sched_critmon_csection(rtcb, false);
+#endif
+#ifdef CONFIG_SCHED_INSTRUMENTATION_CSECTION
               sched_note_csection(rtcb, false);
 #endif
               /* Decrement our count on the lock.  If all CPUs have
@@ -563,7 +576,10 @@ void leave_critical_section(irqstate_t flags)
 
   up_irq_restore(flags);
 }
-#else /* defined(CONFIG_SCHED_INSTRUMENTATION_CSECTION) */
+
+#else /* defined(CONFIG_SCHED_INSTRUMENTATION_CSECTION) ||
+       * defined(CONFIG_SCHED_CRITMONITOR) */
+
 void leave_critical_section(irqstate_t flags)
 {
   /* Check if we were called from an interrupt handler and that the tasks
@@ -577,7 +593,12 @@ void leave_critical_section(irqstate_t flags)
 
       /* Yes.. Note that we have left the critical section */
 
+#ifdef CONFIG_SCHED_CRITMONITOR
+      sched_critmon_csection(rtcb, false);
+#endif
+#ifdef CONFIG_SCHED_INSTRUMENTATION_CSECTION
       sched_note_csection(rtcb, false);
+#endif
     }
 
   /* Restore the previous interrupt state. */
@@ -669,4 +690,5 @@ bool irq_cpu_locked(int cpu)
 }
 #endif
 
-#endif /* CONFIG_SMP || CONFIG_SCHED_INSTRUMENTATION_CSECTION */
+#endif /* CONFIG_SMP || CONFIG_SCHED_INSTRUMENTATION_CSECTION ||
+        * CONFIG_SCHED_CRITMONITOR */

sched/sched/Make.defs

@@ -73,6 +73,8 @@ ifeq ($(CONFIG_SCHED_SPORADIC),y)
 CSRCS += sched_sporadic.c sched_suspendscheduler.c
 else ifeq ($(CONFIG_SCHED_INSTRUMENTATION),y)
 CSRCS += sched_suspendscheduler.c
+else ifeq ($(CONFIG_SCHED_CRITMONITOR),y)
+CSRCS += sched_suspendscheduler.c
 endif
 
 ifneq ($(CONFIG_RR_INTERVAL),0)
@@ -81,6 +83,8 @@ else ifeq ($(CONFIG_SCHED_SPORADIC),y)
 CSRCS += sched_resumescheduler.c
 else ifeq ($(CONFIG_SCHED_INSTRUMENTATION),y)
 CSRCS += sched_resumescheduler.c
+else ifeq ($(CONFIG_SCHED_CRITMONITOR),y)
+CSRCS += sched_resumescheduler.c
 else ifeq ($(CONFIG_SMP),y)
 CSRCS += sched_resumescheduler.c
 endif
@@ -101,10 +105,6 @@ else
 CSRCS += sched_processtimer.c
 endif
 
-ifeq ($(CONFIG_SCHED_INSTRUMENTATION_BUFFER),y)
-CSRCS += sched_note.c
-endif
-
 ifeq ($(CONFIG_SMP),y)
 CSRCS += sched_tasklistlock.c
 ifeq ($(CONFIG_ARCH_GLOBAL_IRQDISABLE),y)
@@ -114,6 +114,14 @@ CSRCS += sched_thistask.c
 endif
 endif
 
+ifeq ($(CONFIG_SCHED_INSTRUMENTATION_BUFFER),y)
+CSRCS += sched_note.c
+endif
+
+ifeq ($(CONFIG_SCHED_CRITMONITOR),y)
+CSRCS += sched_critmonitor.c
+endif
+
 # Include sched build support
 
 DEPPATH += --dep-path sched

sched/sched/sched.h

@@ -496,6 +496,15 @@ void sched_tasklist_unlock(irqstate_t lock);
 void weak_function sched_process_cpuload(void);
 #endif
 
+/* Critical section monitor */
+
+#ifdef CONFIG_SCHED_CRITMONITOR
+void sched_critmon_preemption(FAR struct tcb_s *tcb, bool state);
+void sched_critmon_csection(FAR struct tcb_s *tcb, bool state);
+void sched_critmon_resume(FAR struct tcb_s *tcb);
+void sched_critmon_suspend(FAR struct tcb_s *tcb);
+#endif
+
 /* TCB operations */
 
 bool sched_verifytcb(FAR struct tcb_s *tcb);

sched/sched/sched_critmonitor.c

@@ -0,0 +1,249 @@
+/****************************************************************************
+ * sched/sched/sched_critmonitor.c
+ *
+ *   Copyright (C) 2018 Gregory Nutt. All rights reserved.
+ *   Author: Gregory Nutt <gnutt@nuttx.org>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ * 3. Neither the name NuttX nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ ****************************************************************************/
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <sys/types.h>
+#include <sched.h>
+#include "sched/sched.h"
+
+#ifdef CONFIG_SCHED_CRITMONITOR
+
+/****************************************************************************
+ * Pre-processor Definitions
+ ****************************************************************************/
+
+/* Flags used by the critical section monitor */
+
+#define CRITMON_PREEMPT  (1 << 0)  /* Bit 0:  Pre-emption is disabled */
+#define CRITMON_CSECTION (1 << 1)  /* Bit 1:  In a critical section */
+
+#define DISABLE_PREEMPT(t)  do { (t)->flags |= CRITMON_PREEMPT; } while (0)
+#define ENTER_CSECTION(t)   do { (t)->flags |= CRITMON_PREEMPT; } while (0)
+
+#define ENABLE_PREEMPT(t)   do { (t)->flags &= ~CRITMON_PREEMPT; } while (0)
+#define LEAVE_CSECTION(t)   do { (t)->flags &= ~CRITMON_PREEMPT; } while (0)
+
+#define PREEMPT_DISABLED(t) (((t)->crit_flags & CRITMON_PREEMPT) != 0)
+#define IN_CSECTION(t)      (((t)->crit_flags & CRITMON_CSECTION) != 0)
+
+/****************************************************************************
+ * External Function Prototypes
+ ****************************************************************************/
+
+/* If CONFIG_SCHED_CRITMONITOR is selected, then platform-specific logic
+ * must provide the following interface.  This interface simply provides the
+ * current time value in unknown units.  NOTE:  This function may be called
+ * early before the timer has been initialized.  In that event, the function
+ * should just return a start time of zero.
+ *
+ * Nothing is assumed about the units of this time value.  The following
+ * are assumed, however: (1) The time is an unsigned is an unsigned integer
+ * value, (2) is is monotonically increasing, and (3) the elapsed time
+ * (also in unknown units) can be obtained by subtracting a start time
+ * from the current time.
+ */
+
+uint32_t up_critmon_gettime(void);
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: sched_critmon_preemption
+ *
+ * Description:
+ *   Called when there is any change in pre-emptible state of a thread.
+ *
+ * Assumptions:
+ *   Called within a critical section.
+ *
+ ****************************************************************************/
+
+void sched_critmon_preemption(FAR struct tcb_s *tcb, bool state)
+{
+  /* Are we enabling or disabling pre-emption */
+
+  if (state)
+    {
+      DEBUGASSERT(tcb->premp_start == 0 && !PREEMPT_DISABLED(tcb));
+
+      /* Disabling.. Save the start time */
+
+      tcb->premp_start = up_critmon_gettime();
+      DISABLE_PREEMPT(tcb);
+    }
+  else if (tcb->premp_start != 0)
+    {
+      DEBUGASSERT(PREEMPT_DISABLED(tcb));
+
+      /* Re-enabling.. Check for the max elapsed time */
+
+      uint32_t elapsed = tcb->premp_start - up_critmon_gettime();
+
+      tcb->premp_start = 0;
+      if (elapsed > tcb->premp_max)
+        {
+          tcb->premp_max = elapsed;
+        }
+
+      ENABLE_PREEMPT(tcb);
+    }
+}
+
+/****************************************************************************
+ * Name: sched_critmon_csection
+ *
+ * Description:
+ *   Called when a thread enters or leaves a critical section.
+ *
+ * Assumptions:
+ *   Called within a critical section.
+ *
+ ****************************************************************************/
+
+void sched_critmon_csection(FAR struct tcb_s *tcb, bool state)
+{
+  /* Are we entering or leaving the critical section? */
+
+  if (state)
+    {
+      /* Entering... Save the start time. */
+
+      DEBUGASSERT(tcb->crit_start == 0 && !IN_CSECTION(tcb));
+      tcb->crit_start = up_critmon_gettime();
+    }
+  else if (tcb->crit_start != 0)
+    {
+      DEBUGASSERT(IN_CSECTION(tcb));
+
+      /* Leaving .. Check for the max elapsed time */
+
+      uint32_t elapsed = tcb->crit_start - up_critmon_gettime();
+
+      tcb->crit_start = 0;
+      if (elapsed > tcb->crit_max)
+        {
+          tcb->crit_max = elapsed;
+        }
+
+      ENTER_CSECTION(tcb);
+    }
+}
+
+/****************************************************************************
+ * Name: sched_critmon_resume
+ *
+ * Description:
+ *   Called when a thread resumes execution, perhaps re-establishing a
+ *   critical section or a non-pre-emptible state.
+ *
+ * Assumptions:
+ *   Called within a critical section.
+ *
+ ****************************************************************************/
+
+void sched_critmon_resume(FAR struct tcb_s *tcb)
+{
+  DEBUGASSERT(tcb->premp_start == 0 && tcb->crit_start == 0);
+
+  /* Did this task disable pre-emption? */
+
+  if (PREEMPT_DISABLED(tcb))
+    {
+      /* Yes.. Save the start time */
+
+      tcb->premp_start = up_critmon_gettime();
+    }
+
+  /* Was this task in a critical section? */
+
+  if (IN_CSECTION(tcb))
+    {
+      /* Yes.. Save the start time */
+
+      tcb->crit_start = up_critmon_gettime();
+    }
+}
+
+/****************************************************************************
+ * Name: sched_critmon_suspend
+ *
+ * Description:
+ *   Called when a thread suspends execution, perhaps terminating a
+ *   critical section or a non-pre-emptible state.
+ *
+ * Assumptions:
+ *   Called within a critical section.
+ *
+ ****************************************************************************/
+
+void sched_critmon_suspend(FAR struct tcb_s *tcb)
+{
+  /* Did this task disable pre-emption? */
+
+  if (PREEMPT_DISABLED(tcb))
+    {
+      /* Re-enabling.. Check for the max elapsed time */
+
+      uint32_t elapsed = tcb->premp_start - up_critmon_gettime();
+
+      tcb->premp_start = 0;
+      if (elapsed > tcb->premp_max)
+        {
+          tcb->premp_max = elapsed;
+        }
+    }
+
+  /* Is this task in a critical section? */
+
+  if (IN_CSECTION(tcb))
+    {
+      /* Leaving .. Check for the max elapsed time */
+
+      uint32_t elapsed = tcb->crit_start - up_critmon_gettime();
+
+      tcb->crit_start = 0;
+      if (elapsed > tcb->crit_max)
+        {
+          tcb->crit_max = elapsed;
+        }
+    }
+}
+
+#endif

sched/sched/sched_lock.c

@@ -250,14 +250,20 @@ int sched_lock(void)
       (void)up_fetchsub16(&g_global_lockcount, 1);
 #endif
 
-#ifdef CONFIG_SCHED_INSTRUMENTATION_PREEMPTION
+#if defined(CONFIG_SCHED_INSTRUMENTATION_PREEMPTION) || \
+    defined(CONFIG_SCHED_CRITMONITOR)
       /* Check if we just acquired the lock */
 
       if (rtcb->lockcount == 1)
         {
           /* Note that we have pre-emption locked */
 
+#ifdef CONFIG_SCHED_CRITMONITOR
+          sched_critmon_premption(rtcb, true);
+#endif
+#ifdef CONFIG_SCHED_INSTRUMENTATION_PREEMPTION
           sched_note_premption(rtcb, true);
+#endif
         }
 #endif
 
@@ -299,14 +305,20 @@ int sched_lock(void)
 
       rtcb->lockcount++;
 
-#ifdef CONFIG_SCHED_INSTRUMENTATION_PREEMPTION
+#if defined(CONFIG_SCHED_INSTRUMENTATION_PREEMPTION) || \
+    defined(CONFIG_SCHED_CRITMONITOR)
       /* Check if we just acquired the lock */
 
       if (rtcb->lockcount == 1)
         {
           /* Note that we have pre-emption locked */
 
+#ifdef CONFIG_SCHED_CRITMONITOR
+          sched_critmon_premption(rtcb, true);
+#endif
+#ifdef CONFIG_SCHED_INSTRUMENTATION_PREEMPTION
           sched_note_premption(rtcb, true);
+#endif
         }
 #endif
     }

sched/sched/sched_resumescheduler.c

@@ -1,7 +1,7 @@
 /****************************************************************************
  * sched/sched/sched_resumescheduler.c
  *
- *   Copyright (C) 2015 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2015, 2018 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <gnutt@nuttx.org>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -49,7 +49,8 @@
 #include "sched/sched.h"
 
 #if CONFIG_RR_INTERVAL > 0 || defined(CONFIG_SCHED_SPORADIC) || \
-    defined(CONFIG_SCHED_INSTRUMENTATION) || defined(CONFIG_SMP)
+    defined(CONFIG_SCHED_INSTRUMENTATION) || defined(CONFIG_SCHED_CRITMONITOR) || \
+    defined(CONFIG_SMP)
 
 /****************************************************************************
  * Public Functions
@@ -96,9 +97,12 @@ void sched_resume_scheduler(FAR struct tcb_s *tcb)
     }
 #endif
 
-#ifdef CONFIG_SCHED_INSTRUMENTATION
-  /* Inidicate the task has been resumed */
+  /* Indicate the task has been resumed */
 
+#ifdef CONFIG_SCHED_CRITMONITOR
+  sched_critmon_resume(tcb);
+#endif
+#ifdef CONFIG_SCHED_INSTRUMENTATION
   sched_note_resume(tcb);
 #endif
 
@@ -142,4 +146,5 @@ void sched_resume_scheduler(FAR struct tcb_s *tcb)
 }
 
 #endif /* CONFIG_RR_INTERVAL > 0 || CONFIG_SCHED_SPORADIC || \
-        * CONFIG_SCHED_INSTRUMENTATION || CONFIG_SMP */
+        * CONFIG_SCHED_INSTRUMENTATION || CONFIG_SCHED_CRITMONITOR ||
+        * CONFIG_SMP */

sched/sched/sched_suspendscheduler.c

@@ -1,7 +1,7 @@
 /****************************************************************************
  * sched/sched/sched_suspendscheduler.c
  *
- *   Copyright (C) 2015-2016 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2015-2016, 2018 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <gnutt@nuttx.org>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -50,7 +50,8 @@
 #include "clock/clock.h"
 #include "sched/sched.h"
 
-#if defined(CONFIG_SCHED_SPORADIC) || defined(CONFIG_SCHED_INSTRUMENTATION)
+#if defined(CONFIG_SCHED_SPORADIC) || defined(CONFIG_SCHED_INSTRUMENTATION) || \
+    defined(CONFIG_SCHED_CRITMONITOR)
 
 /****************************************************************************
  * Public Functions
@@ -83,11 +84,15 @@ void sched_suspend_scheduler(FAR struct tcb_s *tcb)
     }
 #endif
 
-#ifdef CONFIG_SCHED_INSTRUMENTATION
-  /* Inidicate the task has been suspended */
+  /* Indicate that the task has been suspended */
 
+#ifdef CONFIG_SCHED_CRITMONITOR
+  sched_critmon_suspend(tcb);
+#endif
+#ifdef CONFIG_SCHED_INSTRUMENTATION
   sched_note_suspend(tcb);
 #endif
 }
 
-#endif /* CONFIG_SCHED_SPORADIC || CONFIG_SCHED_INSTRUMENTATION */
+#endif /* CONFIG_SCHED_SPORADIC || CONFIG_SCHED_INSTRUMENTATION ||
+        * CONFIG_SCHED_CRITMONITOR */

sched/sched/sched_unlock.c

@@ -103,11 +103,15 @@ int sched_unlock(void)
 
       if (rtcb->lockcount <= 0)
         {
-#ifdef CONFIG_SCHED_INSTRUMENTATION_PREEMPTION
           /* Note that we no longer have pre-emption disabled. */
 
+#ifdef CONFIG_SCHED_CRITMONITOR
+          sched_critmon_premption(rtcb, false);
+#endif
+#ifdef CONFIG_SCHED_INSTRUMENTATION_PREEMPTION
           sched_note_premption(rtcb, false);
 #endif
+
           /* Set the lock count to zero */
 
           rtcb->lockcount = 0;
@@ -254,11 +258,15 @@ int sched_unlock(void)
 
       if (rtcb->lockcount <= 0)
         {
-#ifdef CONFIG_SCHED_INSTRUMENTATION_PREEMPTION
           /* Note that we no longer have pre-emption disabled. */
 
+#ifdef CONFIG_SCHED_CRITMONITOR
+          sched_critmon_premption(rtcb, false);
+#endif
+#ifdef CONFIG_SCHED_INSTRUMENTATION_PREEMPTION
           sched_note_premption(rtcb, false);
 #endif
+
           /* Set the lock count to zero */
 
           rtcb->lockcount = 0;