Re: [PATCH] drm/amdkfd: use time_is_before_jiffies(a + b) to replace "jiffies - a > b"

From: Yu Zhe
Date: Wed Jul 27 2022 - 22:20:40 EST


在 2022年07月28日 00:04, Felix Kuehling 写道:

This patch introduces a build warning for me:
CC [M] drivers/gpu/drm/amd/amdgpu/../amdkfd/kfd_interrupt.o
In file included from /home/fkuehlin/compute/kernel/include/linux/spinlock.h:54,
from /home/fkuehlin/compute/kernel/include/linux/mmzone.h:8,
from /home/fkuehlin/compute/kernel/include/linux/gfp.h:6,
from /home/fkuehlin/compute/kernel/include/linux/slab.h:15,
from /home/fkuehlin/compute/kernel/drivers/gpu/drm/amd/amdgpu/../amdkfd/kfd_interrupt.c:44:
/home/fkuehlin/compute/kernel/drivers/gpu/drm/amd/amdgpu/../amdkfd/kfd_interrupt.c: In function ?interrupt_wq?:
/home/fkuehlin/compute/kernel/include/linux/typecheck.h:12:18: warning: comparison of distinct pointer types lacks a cast
12 | (void)(&__dummy == &__dummy2); \
| ^~
/home/fkuehlin/compute/kernel/include/linux/jiffies.h:106:3: note: in expansion of macro ?typecheck?
106 | typecheck(unsigned long, b) && \
| ^~~~~~~~~
/home/fkuehlin/compute/kernel/include/linux/jiffies.h:154:35: note: in expansion of macro ?time_after?
154 | #define time_is_before_jiffies(a) time_after(jiffies, a)
| ^~~~~~~~~~
/home/fkuehlin/compute/kernel/drivers/gpu/drm/amd/amdgpu/../amdkfd/kfd_interrupt.c:159:7: note: in expansion of macro ?time_is_before_jiffies?
159 | if (time_is_before_jiffies(start_jiffies + HZ)) {
| ^~~~~~~~~~~~~~~~~~~~~~
I think you need to change the the definition of start_jiffies to be
unsigned long. Do you want to submit a v2 of your patch?

Yes, I will submit v2 patch later.

That said, I think the existing code was fine, though the type-mismatch
highlighted by your patch is a bit iffy.

And if the timer wrap changes in the future you won't have to alter your driver code. So I think it's better.

Regards,
Felix
Am 2022-07-26 um 22:59 schrieb Yu Zhe:
time_is_before_jiffies deals with timer wrapping correctly.
Signed-off-by: Yu Zhe <yuzhe@xxxxxxxxxxxx>
---
drivers/gpu/drm/amd/amdkfd/kfd_interrupt.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_interrupt.c b/drivers/gpu/drm/amd/amdkfd/kfd_interrupt.c
index a9466d154395..6397926e059c 100644
--- a/drivers/gpu/drm/amd/amdkfd/kfd_interrupt.c
+++ b/drivers/gpu/drm/amd/amdkfd/kfd_interrupt.c
@@ -156,7 +156,7 @@ static void interrupt_wq(struct work_struct *work)
while (dequeue_ih_ring_entry(dev, ih_ring_entry)) {
dev->device_info.event_interrupt_class->interrupt_wq(dev,
ih_ring_entry);
- if (jiffies - start_jiffies > HZ) {
+ if (time_is_before_jiffies(start_jiffies + HZ)) {
/* If we spent more than a second processing signals,
* reschedule the worker to avoid soft-lockup warnings
*/