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authorPeter Zijlstra <peterz@infradead.org>2013-08-14 14:55:40 +0200
committerIngo Molnar <mingo@kernel.org>2013-09-25 14:07:50 +0200
commita787870924dbd6f321661e06d4ec1c7a408c9ccf (patch)
tree43aae13f34d21b001efd4a4a4e64f3d085988bad /include/asm-generic/preempt.h
parentf27dde8deef33c9e58027df11ceab2198601d6a6 (diff)
downloadlwn-a787870924dbd6f321661e06d4ec1c7a408c9ccf.tar.gz
lwn-a787870924dbd6f321661e06d4ec1c7a408c9ccf.zip
sched, arch: Create asm/preempt.h
In order to prepare to per-arch implementations of preempt_count move the required bits into an asm-generic header and use this for all archs. Signed-off-by: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/n/tip-h5j0c1r3e3fk015m30h8f1zx@git.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'include/asm-generic/preempt.h')
-rw-r--r--include/asm-generic/preempt.h54
1 files changed, 54 insertions, 0 deletions
diff --git a/include/asm-generic/preempt.h b/include/asm-generic/preempt.h
new file mode 100644
index 000000000000..a1fc6590a743
--- /dev/null
+++ b/include/asm-generic/preempt.h
@@ -0,0 +1,54 @@
+#ifndef __ASM_PREEMPT_H
+#define __ASM_PREEMPT_H
+
+#include <linux/thread_info.h>
+
+/*
+ * We mask the PREEMPT_NEED_RESCHED bit so as not to confuse all current users
+ * that think a non-zero value indicates we cannot preempt.
+ */
+static __always_inline int preempt_count(void)
+{
+ return current_thread_info()->preempt_count & ~PREEMPT_NEED_RESCHED;
+}
+
+static __always_inline int *preempt_count_ptr(void)
+{
+ return &current_thread_info()->preempt_count;
+}
+
+/*
+ * We now loose PREEMPT_NEED_RESCHED and cause an extra reschedule; however the
+ * alternative is loosing a reschedule. Better schedule too often -- also this
+ * should be a very rare operation.
+ */
+static __always_inline void preempt_count_set(int pc)
+{
+ *preempt_count_ptr() = pc;
+}
+
+/*
+ * We fold the NEED_RESCHED bit into the preempt count such that
+ * preempt_enable() can decrement and test for needing to reschedule with a
+ * single instruction.
+ *
+ * We invert the actual bit, so that when the decrement hits 0 we know we both
+ * need to resched (the bit is cleared) and can resched (no preempt count).
+ */
+
+static __always_inline void set_preempt_need_resched(void)
+{
+ *preempt_count_ptr() &= ~PREEMPT_NEED_RESCHED;
+}
+
+static __always_inline void clear_preempt_need_resched(void)
+{
+ *preempt_count_ptr() |= PREEMPT_NEED_RESCHED;
+}
+
+static __always_inline bool test_preempt_need_resched(void)
+{
+ return !(*preempt_count_ptr() & PREEMPT_NEED_RESCHED);
+}
+
+#endif /* __ASM_PREEMPT_H */