Current lock stealing implementation encodes the new owner woken up,
but not yet scheduled state redundantly. First, the XNWAKEN thread bit
is set and, second, the wwake field in xnthread_t points to the
xnsynch_t object that the thread is about to own.
Apparently, no technical benefit can be expected from this. It rather
adds some, though minor, overhead to frequently used core services.
Moreover such redundancy can cause confusion for the uninformed reader
who tries to understand the implementation.
This patch encodes the state purely via wwake (XNWAKEN set = wwake !=
NULL). Compared to the first version posted, this one also clears the
state again in case xnsynch_sleep_on is redone after some lock robbery
(compensating the removed XNWAKEN clearance in xnpod_suspend_thread).
Jan
---
include/nucleus/thread.h |1 -
ksrc/nucleus/pod.c |2 +-
ksrc/nucleus/synch.c | 11 ---
3 files changed, 5 insertions(+), 9 deletions(-)
Index: b/include/nucleus/thread.h
===
--- a/include/nucleus/thread.h
+++ b/include/nucleus/thread.h
@@ -112,7 +112,6 @@
#define XNRMID0x0002 /** Pending on a removed resource */
#define XNBREAK 0x0004 /** Forcibly awaken from a wait state */
#define XNKICKED 0x0008 /** Kicked upon Linux signal (shadow only) */
-#define XNWAKEN 0x0010 /** Thread waken up upon resource availability */
#define XNROBBED 0x0020 /** Robbed from resource ownership */
#define XNATOMIC 0x0040 /** In atomic switch from secondary to primary
mode */
#define XNAFFSET 0x0080 /** CPU affinity changed from primary mode */
Index: b/ksrc/nucleus/pod.c
===
--- a/ksrc/nucleus/pod.c
+++ b/ksrc/nucleus/pod.c
@@ -1406,7 +1406,7 @@ void xnpod_suspend_thread(xnthread_t *th
}
#endif /* CONFIG_XENO_OPT_PERVASIVE */
- xnthread_clear_info(thread, XNRMID | XNTIMEO | XNBREAK |
XNWAKEN | XNROBBED);
+ xnthread_clear_info(thread, XNRMID | XNTIMEO | XNBREAK |
XNROBBED);
}
/* Don't start the timer for a thread indefinitely delayed by
Index: b/ksrc/nucleus/synch.c
===
--- a/ksrc/nucleus/synch.c
+++ b/ksrc/nucleus/synch.c
@@ -199,7 +199,7 @@ redo:
}
if (thread-cprio owner-cprio) {
- if (xnthread_test_info(owner, XNWAKEN) owner-wwake ==
synch) {
+ if (owner-wwake == synch) {
/* Ownership is still pending, steal the resource. */
synch-owner = thread;
xnthread_clear_info(thread, XNRMID | XNTIMEO | XNBREAK);
@@ -225,6 +225,9 @@ redo:
xnpod_suspend_thread(thread, XNPEND, timeout, timeout_mode, synch);
+ /* We are awake, no one must steal our lock anymore. */
+ thread-wwake = NULL;
+
if (xnthread_test_info(thread, XNRMID | XNTIMEO | XNBREAK))
goto unlock_and_exit;
@@ -241,10 +244,6 @@ redo:
}
unlock_and_exit:
-
- thread-wwake = NULL;
- xnthread_clear_info(thread, XNWAKEN);
-
xnlock_put_irqrestore(nklock, s);
}
@@ -389,7 +388,6 @@ xnthread_t *xnsynch_wakeup_one_sleeper(x
thread-wchan = NULL;
thread-wwake = synch;
synch-owner = thread;
- xnthread_set_info(thread, XNWAKEN);
trace_mark(xn_nucleus_synch_wakeup_one,
thread %p thread_name %s synch %p,
thread, xnthread_name(thread), synch);
@@ -503,7 +501,6 @@ xnpholder_t *xnsynch_wakeup_this_sleeper
thread-wchan = NULL;
thread-wwake = synch;
synch-owner = thread;
- xnthread_set_info(thread, XNWAKEN);
trace_mark(xn_nucleus_synch_wakeup_all,
thread %p thread_name %s synch %p,
thread, xnthread_name(thread), synch);
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