[PATCH 7/9] sched: define TIF_ALLOW_RESCHED

Ankur Arora
2023-04-03T05:24:10Z

Define TIF_ALLOW_RESCHED to allow threads to mark themselves as allowing
rescheduling in the irqexit path with PREEMPTION_NONE/_VOLUNTARY.

This is meant to be used for long running tasks where it is
not convenient to periodically call cond_resched().

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
arch/x86/include/asm/thread_info.h | 2 ++
include/linux/sched.h | 29 +++++++++++++++++++++++++++++
2 files changed, 31 insertions(+)

diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index f1cccba52eb9..8c18b9eaeec4 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -100,6 +100,7 @@ struct thread_info {
#define TIF_BLOCKSTEP 25 /* set when we want DEBUGCTLMSR_BTF */
#define TIF_LAZY_MMU_UPDATES 27 /* task is updating the mmu lazily */
#define TIF_ADDR32 29 /* 32-bit address space on 64 bits */
+#define TIF_RESCHED_ALLOW 30 /* can reschedule if needed */

#define _TIF_NOTIFY_RESUME (1 << TIF_NOTIFY_RESUME)
#define _TIF_SIGPENDING (1 << TIF_SIGPENDING)
@@ -122,6 +123,7 @@ struct thread_info {
#define _TIF_BLOCKSTEP (1 << TIF_BLOCKSTEP)
#define _TIF_LAZY_MMU_UPDATES (1 << TIF_LAZY_MMU_UPDATES)
#define _TIF_ADDR32 (1 << TIF_ADDR32)
+#define _TIF_RESCHED_ALLOW (1 << TIF_RESCHED_ALLOW)

/* flags to check in __switch_to() */
#define _TIF_WORK_CTXSW_BASE \
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 63d242164b1a..1e7536e6d9ce 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2229,6 +2229,35 @@ static __always_inline bool need_resched(void)
return unlikely(tif_need_resched());
}

+/*
+ * Define this in common code to avoid include hell.
+ */
+static __always_inline bool resched_allowed(void)
+{
+#ifndef TIF_RESCHED_ALLOW
+ return false;
+#else
+ return unlikely(test_tsk_thread_flag(current, TIF_RESCHED_ALLOW));
+#endif
+}
+
+static inline void allow_resched(void)
+{
+ /*
+ * allow_resched() allows preemption via the irqexit context.
+ * To ensure that we stick around on the current runqueue,
+ * disallow migration.
+ */
+ migrate_disable();
+ set_tsk_thread_flag(current, TIF_RESCHED_ALLOW);
+}
+
+static inline void disallow_resched(void)
+{
+ clear_tsk_thread_flag(current, TIF_RESCHED_ALLOW);
+ migrate_enable();
+}
+
/*
* Wrappers for p->thread_info->cpu access. No-op on UP.
*/
--
2.31.1