[PATCH V4] amdgpu: reduce no need mutex_lock area

[PATCH V4] amdgpu: reduce no need mutex_lock area

[Bernard Zhao]

Maybe we could reduce the mutex_lock(&mem->lock)`s protected code area,
and no need to protect pr_debug.

Signed-off-by: Bernard Zhao <bernard@vivo.com>

Changes since V1:
*commit message improve

Changes since V2:
*move comment along with the mutex_unlock

Changes since V3:
*lock protect the if check, there is some possibility of multi-threaded
 racing modify.

Link for V1:
*https://lore.kernel.org/patchwork/patch/1226588/
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
index 327317c54f7c..549bdb429883 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
@@ -1289,9 +1289,9 @@ int amdgpu_amdkfd_gpuvm_free_memory_of_gpu(
 	mutex_lock(&mem->lock);
 
 	if (mem->mapped_to_gpu_memory > 0) {
+		mutex_unlock(&mem->lock);
 		pr_debug("BO VA 0x%llx size 0x%lx is still mapped.\n",
 				mem->va, bo_size);
-		mutex_unlock(&mem->lock);
 		return -EBUSY;
 	}
 
-- 
2.26.2

Re: [PATCH V4] amdgpu: reduce no need mutex_lock area

[Christian König]

Am 21.04.20 um 09:36 schrieb Bernard Zhao:
> Maybe we could reduce the mutex_lock(&mem->lock)`s protected code area,
> and no need to protect pr_debug.

Well that change looks rather superfluous to me.

This is for freeing memory which by definition can only be done once and 
so the should be exactly zero contention on the lock except in a case of 
an error.

Regards,
Christian.

>
> Signed-off-by: Bernard Zhao <bernard@vivo.com>
>
> Changes since V1:
> *commit message improve
>
> Changes since V2:
> *move comment along with the mutex_unlock
>
> Changes since V3:
> *lock protect the if check, there is some possibility of multi-threaded
>   racing modify.
>
> Link for V1:
> *https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Fpatchwork%2Fpatch%2F1226588%2F&amp;data=02%7C01%7Cchristian.koenig%40amd.com%7C9f2b2080f4174c421e4f08d7e5c6b899%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637230513976133424&amp;sdata=6wezM%2F%2FjM5uuLblJejS9XFlE9DjWQ5zSt5PsqrfvCVo%3D&amp;reserved=0
> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
> index 327317c54f7c..549bdb429883 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
> @@ -1289,9 +1289,9 @@ int amdgpu_amdkfd_gpuvm_free_memory_of_gpu(
>   	mutex_lock(&mem->lock);
>   
>   	if (mem->mapped_to_gpu_memory > 0) {
> +		mutex_unlock(&mem->lock);
>   		pr_debug("BO VA 0x%llx size 0x%lx is still mapped.\n",
>   				mem->va, bo_size);
> -		mutex_unlock(&mem->lock);
>   		return -EBUSY;
>   	}
>   

[add Markus.Elfring in mail list ]Re:Re: [PATCH V4] amdgpu: reduce no need mutex_lock area

[赵军奎]

From: "Christian König" <christian.koenig@amd.com>
Date: 2020-04-21 15:41:27
To:  1587181464-114215-1-git-send-email-bernard@vivo.com,Felix Kuehling <Felix.Kuehling@amd.com>,Alex Deucher <alexander.deucher@amd.com>,"David (ChunMing) Zhou" <David1.Zhou@amd.com>,David Airlie <airlied@linux.ie>,Daniel Vetter <daniel@ffwll.ch>,amd-gfx@lists.freedesktop.org,dri-devel@lists.freedesktop.org,linux-kernel@vger.kernel.org
Cc:  opensource.kernel@vivo.com,Bernard Zhao <bernard@vivo.com>
Subject: Re: [PATCH V4] amdgpu: reduce no need mutex_lock area>Am 21.04.20 um 09:36 schrieb Bernard Zhao:
>> Maybe we could reduce the mutex_lock(&mem->lock)`s protected code area,
>> and no need to protect pr_debug.
>
>Well that change looks rather superfluous to me.
>
>This is for freeing memory which by definition can only be done once and 
>so the should be exactly zero contention on the lock except in a case of 
>an error.
>
>Regards,
>Christian.
>
>>
>> Signed-off-by: Bernard Zhao <bernard@vivo.com>
>>
>> Changes since V1:
>> *commit message improve
>>
>> Changes since V2:
>> *move comment along with the mutex_unlock
>>
>> Changes since V3:
>> *lock protect the if check, there is some possibility of multi-threaded
>>   racing modify.
>>
>> Link for V1:
>> *https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Fpatchwork%2Fpatch%2F1226588%2F&amp;data=02%7C01%7Cchristian.koenig%40amd.com%7C9f2b2080f4174c421e4f08d7e5c6b899%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637230513976133424&amp;sdata=6wezM%2F%2FjM5uuLblJejS9XFlE9DjWQ5zSt5PsqrfvCVo%3D&amp;reserved=0
>> ---
>>   drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
>> index 327317c54f7c..549bdb429883 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
>> @@ -1289,9 +1289,9 @@ int amdgpu_amdkfd_gpuvm_free_memory_of_gpu(
>>   	mutex_lock(&mem->lock);
>>   
>>   	if (mem->mapped_to_gpu_memory > 0) {
>> +		mutex_unlock(&mem->lock);
>>   		pr_debug("BO VA 0x%llx size 0x%lx is still mapped.\n",
>>   				mem->va, bo_size);
>> -		mutex_unlock(&mem->lock);
>>   		return -EBUSY;
>>   	}
>>   
>

add Markus.Elfring in mail list 
Regards,
Bernard