The following commit has been merged into the sched/core branch of tip:
Commit-ID: 0e985e9d22864e29d5d2b3d909ad15134d7f6d46
Gitweb: https://git.kernel.org/tip/0e985e9d22864e29d5d2b3d909ad15134d7f6d46
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate: Thu, 12 Jan 2023 20:44:04 +01:00
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Fri, 13 Jan 2023 11:48:18 +01:00
cpuidle: Add comments about noinstr/__cpuidle usage
Add a few words on noinstr / __cpuidle usage.
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20230112195542.397238052@xxxxxxxxxxxxx
---
drivers/cpuidle/cpuidle.c | 12 ++++++++++++
include/linux/compiler_types.h | 10 ++++++++++
2 files changed, 22 insertions(+)
diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index 73f7d8b..500d172 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c
@@ -252,6 +252,18 @@ noinstr int cpuidle_enter_state(struct cpuidle_device *dev,
instrumentation_begin();
}
+ /*
+ * NOTE!!
+ *
+ * For cpuidle_state::enter() methods that do *NOT* set
+ * CPUIDLE_FLAG_RCU_IDLE RCU will be disabled here and these functions
+ * must be marked either noinstr or __cpuidle.
+ *
+ * For cpuidle_state::enter() methods that *DO* set
+ * CPUIDLE_FLAG_RCU_IDLE this isn't required, but they must mark the
+ * function calling ct_cpuidle_enter() as noinstr/__cpuidle and all
+ * functions called within the RCU-idle region.
+ */
entered_state = target_state->enter(dev, drv, index);
if (WARN_ONCE(!irqs_disabled(), "%ps leaked IRQ state", target_state->enter))
diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
index d785890..dea5bf5 100644
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -239,6 +239,16 @@ struct ftrace_likely_data {
#define noinstr __noinstr_section(".noinstr.text")
+/*
+ * The __cpuidle section is used twofold:
+ *
+ * 1) the original use -- identifying if a CPU is 'stuck' in idle state based
+ * on it's instruction pointer. See cpu_in_idle().
+ *
+ * 2) supressing instrumentation around where cpuidle disables RCU; where the
+ * function isn't strictly required for #1, this is interchangeable with
+ * noinstr.
+ */
#define __cpuidle __noinstr_section(".cpuidle.text")
#endif /* __KERNEL__ */
|