[RFC][PATCH 5/9] loongarch: Provide noinstr sched_clock_read()

Peter Zijlstra
2023-05-08T21:37:09Z

With the intent to provide local_clock_noinstr(), a variant of
local_clock() that's safe to be called from noinstr code (with the
assumption that any such code will already be non-preemptible),
prepare for things by providing a noinstr sched_clock_read() function.

Specifically, preempt_enable_*() calls out to schedule(), which upsets
noinstr validation efforts.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
arch/loongarch/include/asm/loongarch.h | 2 +-
arch/loongarch/kernel/time.c | 6 +++---
2 files changed, 4 insertions(+), 4 deletions(-)

--- a/arch/loongarch/include/asm/loongarch.h
+++ b/arch/loongarch/include/asm/loongarch.h
@@ -1167,7 +1167,7 @@ static __always_inline void iocsr_write6

#ifndef __ASSEMBLY__

-static inline u64 drdtime(void)
+static __always_inline u64 drdtime(void)
{
int rID = 0;
u64 val = 0;
--- a/arch/loongarch/kernel/time.c
+++ b/arch/loongarch/kernel/time.c
@@ -190,9 +190,9 @@ static u64 read_const_counter(struct clo
return drdtime();
}

-static u64 native_sched_clock(void)
+static noinstr u64 sched_clock_read(void)
{
- return read_const_counter(NULL);
+ return drdtime();
}

static struct clocksource clocksource_const = {
@@ -211,7 +211,7 @@ int __init constant_clocksource_init(voi

res = clocksource_register_hz(&clocksource_const, freq);

- sched_clock_register(native_sched_clock, 64, freq);
+ sched_clock_register(sched_clock_read, 64, freq);

pr_info("Constant clock source device register\n");