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

From: Felix Kuehling <felix.kuehling@amd.com>
To: Yu Zhe <yuzhe@nfschina.com>,
	alexander.deucher@amd.com, christian.koenig@amd.com,
	Xinhui.Pan@amd.com, airlied@linux.ie, daniel@ffwll.ch
Cc: amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
	linux-kernel@vger.kernel.org, kernel-janitors@vger.kernel.org,
	liqiong@nfschina.com
Subject: Re: [PATCH] drm/amdkfd: use time_is_before_jiffies(a + b) to replace "jiffies - a > b"
Date: Wed, 27 Jul 2022 12:04:10 -0400	[thread overview]
Message-ID: <17e02cd8-eba1-91b8-2506-91a7893ac967@amd.com> (raw)
In-Reply-To: <20220727025917.22477-1-yuzhe@nfschina.com>

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?

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

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@nfschina.com>
> ---
>   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
>   			 */