[PATCH v2 10/35] entry: irqentry_exit only preempts for TIF_NEED_RESCHED

Ankur Arora
2024-05-28T00:36:19Z

Use __tif_need_resched(RESCHED_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 has already checked the
preempt_count().

Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andy Lutomirski <luto@kernel.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>
---
kernel/entry/common.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/kernel/entry/common.c b/kernel/entry/common.c
index bcb23c866425..c684385921de 100644
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -307,7 +307,16 @@ 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
+ * architectures don't fold TIF_NEED_RESCHED in the
+ * preempt_count. For archs that do, this is already covered
+ * in the conditional above.
+ */
+ if (__tif_need_resched(RESCHED_NOW))
preempt_schedule_irq();
}
}
--
2.31.1