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freebsd-ports/devel/linuxthreads/files/condwait-patch
Tor Egge 60032d4ed7 Add an optional experimental patch that reduce the number of context 
switches on UP systems when the thread waiting on a condition has a
higher priority than the thread signalling the condition.

Bump port revision.
2001-09-09 01:12:47 +00:00

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diff -ru ../../work.orig/linuxthreads-2.2.3_1/condvar.c ./condvar.c
--- ../../work.orig/linuxthreads-2.2.3_1/condvar.c Thu Apr 12 21:02:02 2001
+++ ./condvar.c Wed Jul 18 13:30:47 2001
@@ -55,6 +55,8 @@
return did_remove;
}
+extern int __pthread_mutex_condwait_completelock(pthread_mutex_t *mutex);
+
int pthread_cond_wait(pthread_cond_t *cond, pthread_mutex_t *mutex)
{
volatile pthread_descr self = thread_self();
@@ -74,6 +76,7 @@
/* Register extrication interface */
THREAD_SETMEM(self, p_condvar_avail, 0);
+ THREAD_SETMEM(self, p_condwait_mutex, mutex);
__pthread_set_own_extricate_if(self, &extr);
/* Atomically enqueue thread for waiting, but only if it is not
@@ -121,15 +124,35 @@
if (THREAD_GETMEM(self, p_woken_by_cancel)
&& THREAD_GETMEM(self, p_cancelstate) == PTHREAD_CANCEL_ENABLE) {
THREAD_SETMEM(self, p_woken_by_cancel, 0);
- pthread_mutex_lock(mutex);
+ if (THREAD_GETMEM(self, p_condwait_mutex) == NULL) {
+ if (THREAD_GETMEM(self, p_condwait_extra_restart) != 0) {
+ if (spurious_wakeup_count > 0)
+ spurious_wakeup_count--;
+ else
+ suspend(self);
+ }
+ __pthread_mutex_condwait_completelock(mutex);
+ } else
+ pthread_mutex_lock(mutex);
__pthread_do_exit(PTHREAD_CANCELED, CURRENT_STACK_FRAME);
}
+ if (THREAD_GETMEM(self, p_condwait_mutex) == NULL &&
+ THREAD_GETMEM(self, p_condwait_extra_restart) != 0) {
+ if (spurious_wakeup_count > 0)
+ spurious_wakeup_count--;
+ else
+ suspend(self);
+ }
+
/* Put back any resumes we caught that don't belong to us. */
while (spurious_wakeup_count--)
restart(self);
- pthread_mutex_lock(mutex);
+ if (THREAD_GETMEM(self, p_condwait_mutex) == NULL)
+ __pthread_mutex_condwait_completelock(mutex);
+ else
+ pthread_mutex_lock(mutex);
return 0;
}
@@ -155,6 +178,7 @@
/* Register extrication interface */
THREAD_SETMEM(self, p_condvar_avail, 0);
+ THREAD_SETMEM(self, p_condwait_mutex, mutex);
__pthread_set_own_extricate_if(self, &extr);
/* Enqueue to wait on the condition and check for cancellation. */
@@ -215,15 +239,35 @@
if (THREAD_GETMEM(self, p_woken_by_cancel)
&& THREAD_GETMEM(self, p_cancelstate) == PTHREAD_CANCEL_ENABLE) {
THREAD_SETMEM(self, p_woken_by_cancel, 0);
- pthread_mutex_lock(mutex);
+ if (THREAD_GETMEM(self, p_condwait_mutex) == NULL) {
+ if (THREAD_GETMEM(self, p_condwait_extra_restart) != 0) {
+ if (spurious_wakeup_count > 0)
+ spurious_wakeup_count--;
+ else
+ suspend(self);
+ }
+ __pthread_mutex_condwait_completelock(mutex);
+ } else
+ pthread_mutex_lock(mutex);
__pthread_do_exit(PTHREAD_CANCELED, CURRENT_STACK_FRAME);
}
+ if (THREAD_GETMEM(self, p_condwait_mutex) == NULL &&
+ THREAD_GETMEM(self, p_condwait_extra_restart) != 0) {
+ if (spurious_wakeup_count > 0)
+ spurious_wakeup_count--;
+ else
+ suspend(self);
+ }
+
/* Put back any resumes we caught that don't belong to us. */
while (spurious_wakeup_count--)
restart(self);
- pthread_mutex_lock(mutex);
+ if (THREAD_GETMEM(self, p_condwait_mutex) == NULL)
+ __pthread_mutex_condwait_completelock(mutex);
+ else
+ pthread_mutex_lock(mutex);
return 0;
}
@@ -242,9 +286,27 @@
th = dequeue(&cond->__c_waiting);
__pthread_unlock(&cond->__c_lock);
if (th != NULL) {
- th->p_condvar_avail = 1;
- WRITE_MEMORY_BARRIER();
- restart(th);
+ pthread_mutex_t *mutex = th->p_condwait_mutex;
+ if (th->p_condvar_avail == 0 &&
+ mutex != NULL &&
+ (mutex->__m_kind == PTHREAD_MUTEX_ERRORCHECK_NP ||
+ mutex->__m_kind == PTHREAD_MUTEX_TIMED_NP) &&
+ __pthread_alt_condwait_queuelock(&mutex->__m_lock, th) == 0) {
+ th->p_condwait_mutex = NULL;
+ th->p_condwait_extra_restart = 0;
+ WRITE_MEMORY_BARRIER();
+ th->p_condvar_avail = 1;
+ WRITE_MEMORY_BARRIER();
+ if (th->p_condwait_waitnode.abandoned) {
+ th->p_condwait_extra_restart = 1;
+ WRITE_MEMORY_BARRIER();
+ restart(th);
+ }
+ } else {
+ th->p_condvar_avail = 1;
+ WRITE_MEMORY_BARRIER();
+ restart(th);
+ }
}
return 0;
}
@@ -260,9 +322,27 @@
__pthread_unlock(&cond->__c_lock);
/* Now signal each process in the queue */
while ((th = dequeue(&tosignal)) != NULL) {
- th->p_condvar_avail = 1;
- WRITE_MEMORY_BARRIER();
- restart(th);
+ pthread_mutex_t *mutex = th->p_condwait_mutex;
+ if (th->p_condvar_avail == 0 &&
+ mutex != NULL &&
+ (mutex->__m_kind == PTHREAD_MUTEX_ERRORCHECK_NP ||
+ mutex->__m_kind == PTHREAD_MUTEX_TIMED_NP) &&
+ __pthread_alt_condwait_queuelock(&mutex->__m_lock, th) == 0) {
+ th->p_condwait_mutex = NULL;
+ th->p_condwait_extra_restart = 0;
+ WRITE_MEMORY_BARRIER();
+ th->p_condvar_avail = 1;
+ WRITE_MEMORY_BARRIER();
+ if (th->p_condwait_waitnode.abandoned) {
+ th->p_condwait_extra_restart = 1;
+ WRITE_MEMORY_BARRIER();
+ restart(th);
+ }
+ } else {
+ th->p_condvar_avail = 1;
+ WRITE_MEMORY_BARRIER();
+ restart(th);
+ }
}
return 0;
}
diff -ru ../../work.orig/linuxthreads-2.2.3_1/internals.h ./internals.h
--- ../../work.orig/linuxthreads-2.2.3_1/internals.h Wed Jul 18 07:25:04 2001
+++ ./internals.h Wed Jul 18 10:55:57 2001
@@ -125,6 +125,13 @@
int pr_lock_count;
} pthread_readlock_info;
+
+struct wait_node {
+ struct wait_node *next; /* Next node in null terminated linked list */
+ pthread_descr thr; /* The thread waiting with this node */
+ int abandoned; /* Atomic flag */
+};
+
struct _pthread_descr_struct {
union {
struct {
@@ -189,6 +196,9 @@
hp_timing_t p_cpuclock_offset; /* Initial CPU clock for thread. */
#endif
/* New elements must be added at the end. */
+ pthread_mutex_t *p_condwait_mutex;
+ struct wait_node p_condwait_waitnode;
+ char p_condwait_extra_restart;
} __attribute__ ((aligned(32))); /* We need to align the structure so that
doubles are aligned properly. This is 8
bytes on MIPS and 16 bytes on MIPS64.
diff -ru ../../work.orig/linuxthreads-2.2.3_1/mutex.c ./mutex.c
--- ../../work.orig/linuxthreads-2.2.3_1/mutex.c Sun Jan 7 04:35:20 2001
+++ ./mutex.c Wed Jul 18 09:09:13 2001
@@ -92,6 +92,24 @@
}
strong_alias (__pthread_mutex_trylock, pthread_mutex_trylock)
+int __pthread_mutex_condwait_completelock(pthread_mutex_t *mutex)
+{
+ pthread_descr self;
+
+ switch(mutex->__m_kind) {
+ case PTHREAD_MUTEX_ERRORCHECK_NP:
+ self = thread_self();
+ if (mutex->__m_owner == self) return EDEADLK;
+ mutex->__m_owner = self;
+ return 0;
+ case PTHREAD_MUTEX_TIMED_NP:
+ return 0;
+ default:
+ return EINVAL;
+ }
+}
+
+
int __pthread_mutex_lock(pthread_mutex_t * mutex)
{
pthread_descr self;
diff -ru ../../work.orig/linuxthreads-2.2.3_1/spinlock.c ./spinlock.c
--- ../../work.orig/linuxthreads-2.2.3_1/spinlock.c Wed Jul 18 07:25:04 2001
+++ ./spinlock.c Wed Jul 18 10:56:34 2001
@@ -232,12 +232,6 @@
*/
-struct wait_node {
- struct wait_node *next; /* Next node in null terminated linked list */
- pthread_descr thr; /* The thread waiting with this node */
- int abandoned; /* Atomic flag */
-};
-
static long wait_node_free_list;
#if !defined HAS_COMPARE_AND_SWAP || defined TEST_FOR_COMPARE_AND_SWAP
static int wait_node_free_list_spinlock;
@@ -360,6 +354,55 @@
}
#endif
+
+int __pthread_alt_condwait_queuelock(struct _pthread_fastlock * lock,
+ pthread_descr th)
+{
+#if defined HAS_COMPARE_AND_SWAP
+ long oldstatus, newstatus;
+#endif
+
+#if defined TEST_FOR_COMPARE_AND_SWAP
+ if (!__pthread_has_cas)
+#endif
+#if !defined HAS_COMPARE_AND_SWAP || defined TEST_FOR_COMPARE_AND_SWAP
+ {
+ __pthread_acquire(&lock->__spinlock);
+
+ if (lock->__status == 0) {
+ WRITE_MEMORY_BARRIER();
+ lock->__spinlock = __LT_SPINLOCK_INIT;
+ return 1;
+ }
+ th->p_condwait_waitnode.abandoned = 0;
+ th->p_condwait_waitnode.next = (struct wait_node *) lock->__status;
+ th->p_condwait_waitnode.thr = th;
+ lock->__status = (long) &th->p_condwait_waitnode;
+
+ WRITE_MEMORY_BARRIER();
+ lock->__spinlock = __LT_SPINLOCK_INIT;
+ return 0;
+ }
+#endif
+
+#if defined HAS_COMPARE_AND_SWAP
+ do {
+ oldstatus = lock->__status;
+ if (oldstatus == 0) {
+ return 1;
+ }
+ th->p_condwait_waitnode.thr = th;
+ newstatus = (long) &th->p_condwait_waitnode;
+ th->p_condwait_waitnode.abandoned = 0;
+ th->p_condwait_waitnode.next = (struct wait_node *) oldstatus;
+ /* Make sure the store in wait_node.next completes before performing
+ the compare-and-swap */
+ MEMORY_BARRIER();
+ } while(! __compare_and_swap(&lock->__status, oldstatus, newstatus));
+ return 0;
+#endif
+}
+
void __pthread_alt_lock(struct _pthread_fastlock * lock,
pthread_descr self)
diff -ru ../../work.orig/linuxthreads-2.2.3_1/spinlock.h ./spinlock.h
--- ../../work.orig/linuxthreads-2.2.3_1/spinlock.h Wed Jul 18 07:25:04 2001
+++ ./spinlock.h Wed Jul 18 09:14:58 2001
@@ -130,6 +130,9 @@
timed-out waits. Warning: do not mix these operations with the above ones
over the same lock object! */
+extern int __pthread_alt_condwait_queuelock(struct _pthread_fastlock * lock,
+ pthread_descr th);
+
extern void __pthread_alt_lock(struct _pthread_fastlock * lock,
pthread_descr self);
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