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Subject: [PATCH 02/30] thread_info: selector for TIF_NEED_RESCHED[_LAZY]
Date: Mon, 12 Feb 2024 21:55:26 -0800
Message-Id: <20240213055554.1802415-3-ankur.a.arora@oracle.com>
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Define tif_resched() to serve as selector for the specific
need-resched flag: tif_resched(NR_now) mapping to TIF_NEED_RESCHED
and tif_resched(NR_lazy) to TIF_NEED_RESCHED_LAZY.

Note that, for !CONFIG_PREEMPT_AUTO, tif_resched() always evaluates
to TIF_NEED_RESCHED, preserving existing scheduling behaviour.

Cc: Peter Ziljstra <peterz@infradead.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/thread_info.h | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h
index 7b1d9185aac6..99043cbbb6b0 100644
--- a/include/linux/thread_info.h
+++ b/include/linux/thread_info.h
@@ -67,6 +67,30 @@ enum syscall_work_bit {
 #define _TIF_NEED_RESCHED_LAZY _TIF_NEED_RESCHED
 #endif
 
+#define TIF_NEED_RESCHED_LAZY_OFFSET (TIF_NEED_RESCHED_LAZY - TIF_NEED_RESCHED)
+
+typedef enum {
+	NR_now = 0,
+	NR_lazy = 1,
+} resched_t;
+
+/*
+ * tif_resched(r) maps to TIF_NEED_RESCHED[_LAZY] with CONFIG_PREEMPT_AUTO.
+ *
+ * With !CONFIG_PREEMPT_AUTO, both tif_resched(NR_now) and tif_resched(NR_lazy)
+ * reduce to the same value (TIF_NEED_RESCHED) leaving any scheduling behaviour
+ * unchanged.
+ */
+static inline int tif_resched(resched_t rs)
+{
+	return TIF_NEED_RESCHED + rs * TIF_NEED_RESCHED_LAZY_OFFSET;
+}
+
+static inline int _tif_resched(resched_t rs)
+{
+	return 1 << tif_resched(rs);
+}
+
 #ifdef __KERNEL__
 
 #ifndef arch_set_restart_data
-- 
2.31.1