[PATCH RT 1/3] asm-generic/preempt: also check preempt_lazy_count for should_resched() etc.

Jisheng Zhang
2023-05-10T16:35:29Z

lazy preempt count is great mechanism to help ordinary SCHED_OTHER
tasks' throughput Under PREEMPT_RT. But current implementation relies
on each arch-specific code to check the preempt_lazy_count in
should_resched() and __preempt_count_dec_and_test(), if the arch, e.g
riscv use the asm-generic preempt implementation, it losts the great
lazy preempt mechanism.

Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
---
include/asm-generic/preempt.h | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/include/asm-generic/preempt.h b/include/asm-generic/preempt.h
index b4d43a4af5f7..b583e7c38ccf 100644
--- a/include/asm-generic/preempt.h
+++ b/include/asm-generic/preempt.h
@@ -59,6 +59,11 @@ static __always_inline void __preempt_count_sub(int val)
*preempt_count_ptr() -= val;
}

+#ifdef CONFIG_PREEMPT_LAZY
+#define preempt_lazy_count() (current_thread_info()->preempt_lazy_count)
+#else
+#define preempt_lazy_count() (0)
+#endif
static __always_inline bool __preempt_count_dec_and_test(void)
{
/*
@@ -66,7 +71,7 @@ static __always_inline bool __preempt_count_dec_and_test(void)
* operations; we cannot use PREEMPT_NEED_RESCHED because it might get
* lost.
*/
- return !--*preempt_count_ptr() && tif_need_resched();
+ return !--*preempt_count_ptr() && !preempt_lazy_count() && tif_need_resched();
}

/*
@@ -75,6 +80,7 @@ static __always_inline bool __preempt_count_dec_and_test(void)
static __always_inline bool should_resched(int preempt_offset)
{
return unlikely(preempt_count() == preempt_offset &&
+ !preempt_lazy_count() &&
tif_need_resched());
}

--
2.40.1