[PATCH 08/30] entry: irqentry_exit only preempts for TIF_NEED_RESCHED

[Ankur Arora]

Use tif_need_resched(NR_now) instead of need_resched() to be explicit
that this path only reschedules if it is needed imminently.

Also, add a comment about why we need a need-resched check here at
all, given that the top level conditional already has checked the
preempt_count().

Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Originally-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/lkml/87jzshhexi.ffs@tglx/
Signed-off-by: Ankur Arora <ankur.a.arora@xxxxxxxxxx>
---
 kernel/entry/common.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/kernel/entry/common.c b/kernel/entry/common.c
index 5c5befb05410..e1e6d7c92ca2 100644
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -301,7 +301,15 @@ void raw_irqentry_exit_cond_resched(void)
 		rcu_irq_exit_check_preempt();
 		if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
 			WARN_ON_ONCE(!on_thread_stack());
-		if (need_resched())
+
+		/*
+		 * Check if we need to preempt eagerly.
+		 *
+		 * Note we need an explicit check here because some archs don't
+		 * fold TIF_NEED_RESCHED in the preempt_count. For archs that
+		 * do, this is already covered in the conditinal above.
+		 */
+		if (tif_need_resched(NR_now))
 			preempt_schedule_irq();
 	}
 }
-- 
2.31.1