[PATCH v2 06/35] thread_info: define __tif_need_resched(resched_t)

Ankur Arora
2024-05-28T00:36:10Z

Define __tif_need_resched() which takes a resched_t parameter to
decide the immediacy of the need-resched.

Update need_resched() and should_resched() so they both check for
__tif_need_resched(RESCHED_NOW), which keeps the current semantics.

Non scheduling code -- which only cares about any immediately required
preemption -- can continue unchanged since the commonly used interfaces
(need_resched(), should_resched(), tif_need_resched()) stay the same.

This also allows lazy preemption to just be a scheduler detail.

Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Rafael J. Wysocki" <rafael@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Originally-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/lkml/87jzshhexi.ffs@tglx/
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
include/linux/preempt.h | 2 +-
include/linux/sched.h | 7 ++++++-
include/linux/thread_info.h | 34 ++++++++++++++++++++++++++++------
kernel/trace/trace.c | 2 +-
4 files changed, 36 insertions(+), 9 deletions(-)

diff --git a/include/linux/preempt.h b/include/linux/preempt.h
index ce76f1a45722..d453f5e34390 100644
--- a/include/linux/preempt.h
+++ b/include/linux/preempt.h
@@ -312,7 +312,7 @@ do { \
} while (0)
#define preempt_fold_need_resched() \
do { \
- if (tif_need_resched()) \
+ if (__tif_need_resched(RESCHED_NOW)) \
set_preempt_need_resched(); \
} while (0)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 4808e5dd4f69..37a51115b691 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2062,7 +2062,12 @@ extern int __cond_resched_rwlock_write(rwlock_t *lock);

static __always_inline bool need_resched(void)
{
- return unlikely(tif_need_resched());
+ return unlikely(__tif_need_resched(RESCHED_NOW));
+}
+
+static __always_inline bool need_resched_lazy(void)
+{
+ return unlikely(__tif_need_resched(RESCHED_LAZY));
}

/*
diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h
index 65e5beedc915..e246b01553a5 100644
--- a/include/linux/thread_info.h
+++ b/include/linux/thread_info.h
@@ -216,22 +216,44 @@ static __always_inline unsigned long read_ti_thread_flags(struct thread_info *ti

#ifdef _ASM_GENERIC_BITOPS_INSTRUMENTED_NON_ATOMIC_H

-static __always_inline bool tif_need_resched(void)
+static __always_inline bool __tif_need_resched_bitop(int nr_flag)
{
- return arch_test_bit(TIF_NEED_RESCHED,
- (unsigned long *)(&current_thread_info()->flags));
+ return arch_test_bit(nr_flag,
+ (unsigned long *)(&current_thread_info()->flags));
}

#else

-static __always_inline bool tif_need_resched(void)
+static __always_inline bool __tif_need_resched_bitop(int nr_flag)
{
- return test_bit(TIF_NEED_RESCHED,
- (unsigned long *)(&current_thread_info()->flags));
+ return test_bit(nr_flag,
+ (unsigned long *)(&current_thread_info()->flags));
}

#endif /* _ASM_GENERIC_BITOPS_INSTRUMENTED_NON_ATOMIC_H */

+static __always_inline bool __tif_need_resched(resched_t rs)
+{
+ /*
+ * With !PREEMPT_AUTO, this check is only meaningful if we
+ * are checking if tif_resched(RESCHED_NOW) is set.
+ */
+ if (IS_ENABLED(CONFIG_PREEMPT_AUTO) || rs == RESCHED_NOW)
+ return __tif_need_resched_bitop(tif_resched(rs));
+ else
+ return false;
+}
+
+static __always_inline bool tif_need_resched(void)
+{
+ return __tif_need_resched(RESCHED_NOW);
+}
+
+static __always_inline bool tif_need_resched_lazy(void)
+{
+ return __tif_need_resched(RESCHED_LAZY);
+}
+
#ifndef CONFIG_HAVE_ARCH_WITHIN_STACK_FRAMES
static inline int arch_within_stack_frames(const void * const stack,
const void * const stackend,
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 233d1af39fff..ed229527be05 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2511,7 +2511,7 @@ unsigned int tracing_gen_ctx_irq_test(unsigned int irqs_status)
if (softirq_count() >> (SOFTIRQ_SHIFT + 1))
trace_flags |= TRACE_FLAG_BH_OFF;

- if (tif_need_resched())
+ if (__tif_need_resched(RESCHED_NOW))
trace_flags |= TRACE_FLAG_NEED_RESCHED;
if (test_preempt_need_resched())
trace_flags |= TRACE_FLAG_PREEMPT_RESCHED;
--
2.31.1