Changeset 5b03a72 in mainline

Timestamp:

2012-07-29T17:53:48Z (13 years ago)

Author:

Adam Hraska <adam.hraska+hos@…>

Branches:

lfn, master, serial, ticket/834-toolchain-update, topic/msim-upgrade, topic/simplify-dev-export

Children:

f0fcb04

Parents:

8e3ed06

Message:

rcu: Switched from using THREAD→nesting_cnt to CPU→nesting_cnt as the main nesting count variable. RCU no longer has to mess with pointers to the corrent nesting_cnt (and gets rid of one level of indirection when accessing the nesting count in reader sections).

Location:

kernel/generic

Files:

• include/synch/rcu.h (modified) (2 diffs)
• include/synch/rcu_types.h (modified) (2 diffs)
• src/synch/rcu.c (modified) (8 diffs)

kernel/generic/include/synch/rcu.h

@@ -181 +181 @@
 
         /* Record a QS if not in a reader critical section. */
-        if (0 == *CPU->rcu.pnesting_cnt)
+        if (0 == CPU->rcu.nesting_cnt)
                 _rcu_record_qs();
 
-        ++(*CPU->rcu.pnesting_cnt);
+        ++CPU->rcu.nesting_cnt;
 
         preemption_enable();
@@ -195 +195 @@
         preemption_disable();
         
-        if (0 == --(*CPU->rcu.pnesting_cnt)) {
+        if (0 == --CPU->rcu.nesting_cnt) {
                 _rcu_record_qs();
                 

kernel/generic/include/synch/rcu_types.h

@@ -61 +61 @@
         rcu_gp_t last_seen_gp;
         
-        /** Pointer to the currently used nesting count (THREAD's or CPU's). */
-        size_t *pnesting_cnt;
-        /** Temporary nesting count if THREAD is NULL, eg in scheduler(). */
-        size_t tmp_nesting_cnt;
+        /** The number of times an RCU reader section is nested on this cpu. 
+         * 
+         * If positive, it is definitely executing reader code. If zero, 
+         * the thread might already be executing reader code thanks to
+         * cpu instruction reordering.
+         */
+        size_t nesting_cnt;
 
         /** Callbacks to invoke once the current grace period ends, ie cur_cbs_gp.
@@ -128 +131 @@
 /** RCU related per-thread data. */
 typedef struct rcu_thread_data {
-        /** The number of times an RCU reader section is nested. 
-         * 
-         * If positive, it is definitely executing reader code. If zero, 
-         * the thread might already be executing reader code thanks to
-         * cpu instruction reordering.
+        /** 
+         * Nesting count of the thread's RCU read sections when the thread 
+         * is not running.
          */
         size_t nesting_cnt;

kernel/generic/src/synch/rcu.c

@@ -225 +225 @@
         CPU->rcu.last_seen_gp = 0;
         
-        CPU->rcu.pnesting_cnt = &CPU->rcu.tmp_nesting_cnt;
-        CPU->rcu.tmp_nesting_cnt = 0;
+        CPU->rcu.nesting_cnt = 0;
         
         CPU->rcu.cur_cbs = 0;
@@ -286 +285 @@
          * reader section nesting count while we examine/process it.
          */
-        ASSERT(&CPU->rcu.tmp_nesting_cnt == CPU->rcu.pnesting_cnt);
-        
-        /* 
-         * The thread forgot to exit its reader critical secion. 
+        
+        /* 
+         * The thread forgot to exit its reader critical section. 
          * It is a bug, but rather than letting the entire system lock up
          * forcefully leave the reader section. The thread is not holding 
@@ -373 +371 @@
 {
         preemption_disable();
-        bool locked = 0 < *CPU->rcu.pnesting_cnt;
+        bool locked = 0 < CPU->rcu.nesting_cnt;
         preemption_enable();
         
@@ -483 +481 @@
 {
         /* Calling from a reader section will deadlock. */
-        ASSERT(THREAD == 0 || 0 == THREAD->rcu.nesting_cnt);
+        ASSERT(0 == CPU->rcu.nesting_cnt);
         
         synch_item_t completion; 
@@ -1199 +1197 @@
         if (CPU->rcu.last_seen_gp != _rcu_cur_gp) {
                 /* Interrupted a reader in a reader critical section. */
-                if (0 < (*CPU->rcu.pnesting_cnt)) {
+                if (0 < CPU->rcu.nesting_cnt) {
                         ASSERT(!CPU->idle);
                         /* Note to notify the detector from rcu_read_unlock(). */
@@ -1276 +1274 @@
 {
         ASSERT(interrupts_disabled());
-        ASSERT(CPU->rcu.pnesting_cnt == &THREAD->rcu.nesting_cnt);
+        
+        /* Save the thread's nesting count when its not running. */
+        THREAD->rcu.nesting_cnt = CPU->rcu.nesting_cnt;
+        /* Interrupt handlers might use RCU while idle in scheduler(). */
+        CPU->rcu.nesting_cnt = 0;
         
         /* Preempted a reader critical section for the first time. */
@@ -1317 +1319 @@
         
         /* 
-         * After this point THREAD is 0 and stays 0 until the scheduler()
-         * switches to a new thread. Use a temporary nesting counter for readers
-         * in handlers of interrupts that are raised while idle in the scheduler.
-         */
-        CPU->rcu.pnesting_cnt = &CPU->rcu.tmp_nesting_cnt;
-
-        /* 
          * Forcefully associate the detector with the highest priority
          * even if preempted due to its time slice running out.
@@ -1355 +1350 @@
 {
         ASSERT(PREEMPTION_DISABLED || interrupts_disabled());
-        ASSERT(&CPU->rcu.tmp_nesting_cnt == CPU->rcu.pnesting_cnt);
-        
-        CPU->rcu.pnesting_cnt = &THREAD->rcu.nesting_cnt;
+        ASSERT(0 == CPU->rcu.nesting_cnt);
+        
+        /* Load the thread's saved nesting count from before it was preempted. */
+        CPU->rcu.nesting_cnt = THREAD->rcu.nesting_cnt;
 }