Le 10/11/2021 à 21:24, Valentin Schneider a écrit :
CONFIG_PREEMPT{_NONE, _VOLUNTARY} designate either:
o The build-time preemption model when !PREEMPT_DYNAMIC
o The default boot-time preemption model when PREEMPT_DYNAMIC
IOW, using those on PREEMPT_DYNAMIC kernels is meaningless - the actual
model could have been set to something else by the "preempt=foo" cmdline
parameter.
Introduce a set of helpers to determine the actual preemption mode used by
the live kernel.
Suggested-by: Marco Elver <elver@xxxxxxxxxx>
Signed-off-by: Valentin Schneider <valentin.schneider@xxxxxxx>
---
include/linux/sched.h | 16 ++++++++++++++++
kernel/sched/core.c | 11 +++++++++++
2 files changed, 27 insertions(+)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 5f8db54226af..0640d5622496 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2073,6 +2073,22 @@ static inline void cond_resched_rcu(void)
#endif
}
+#ifdef CONFIG_PREEMPT_DYNAMIC
+
+extern bool is_preempt_none(void);
+extern bool is_preempt_voluntary(void);
+extern bool is_preempt_full(void);
Those are trivial tests supposed to be used in fast pathes. They should
be static inlines in order to minimise the overhead.
+
+#else
+
+#define is_preempt_none() IS_ENABLED(CONFIG_PREEMPT_NONE)
+#define is_preempt_voluntary() IS_ENABLED(CONFIG_PREEMPT_VOLUNTARY)
+#define is_preempt_full() IS_ENABLED(CONFIG_PREEMPT)
Would be better to use static inlines here as well instead of macros.
+
+#endif
+
+#define is_preempt_rt() IS_ENABLED(CONFIG_PREEMPT_RT)
+
/*
* Does a critical section need to be broken due to another
* task waiting?: (technically does not depend on CONFIG_PREEMPTION,
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 97047aa7b6c2..9db7f77e53c3 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6638,6 +6638,17 @@ static void __init preempt_dynamic_init(void)
}
}
+#define PREEMPT_MODE_ACCESSOR(mode) \
+ bool is_preempt_##mode(void) \
+ { \
+ WARN_ON_ONCE(preempt_dynamic_mode == preempt_dynamic_undefined); \
Not sure using WARN_ON is a good idea here, as it may be called very
early, see comment on powerpc patch.
+ return preempt_dynamic_mode == preempt_dynamic_##mode; \
+ }
I'm not sure that's worth a macro. You only have 3 accessors, 2 lines of
code each. Just define all 3 in plain text.
CONFIG_PREEMPT_DYNAMIC is based on using strategies like static_calls in
order to minimise the overhead. For those accessors you should use the
same kind of approach and use things like jump_labels in order to not
redo the test at each time and minimise overhead as much as possible.
+
+PREEMPT_MODE_ACCESSOR(none)
+PREEMPT_MODE_ACCESSOR(voluntary)
+PREEMPT_MODE_ACCESSOR(full)
+
#else /* !CONFIG_PREEMPT_DYNAMIC */
static inline void preempt_dynamic_init(void) { }
