[PATCH] drm/amdkfd: Asynchronously free events

[Felix Kuehling]

Am 2022-04-11 um 08:52 schrieb philip yang:
>
>
> On 2022-04-07 22:39, Felix Kuehling wrote:
>> The synchronize_rcu call in destroy_events can take several ms, which
>> noticeably slows down applications destroying many events. Use kfree_rcu
>> to free the event structure asynchronously and eliminate the
>> synchronize_rcu call in the user thread.
>
> Will need similar fix in kfd_smi_ev_release, as I noticed sometime it 
> is slower to exit the app receiving SMI event.
>
> Reviewed-by: Philip Yang <Philip.Yang at amd.com>
>
Thanks. In the case of kfd_smi_ev_release you'd need to use call_rcu 
because it's more than a simple kfree when you're freeing the 
client->fifo. That would have some implications for module unloading, 
too. Maybe you can simplify it by using DECLARE_KFIFO in struct 
kfd_smi_client, since we create the fifo with a fixed size anway. That 
way the cleanup is just a kfree_rcu(client).

Regards,
   Felix


>> Signed-off-by: Felix Kuehling<Felix.Kuehling at amd.com>
>> ---
>>   drivers/gpu/drm/amd/amdkfd/kfd_events.c | 3 +--
>>   drivers/gpu/drm/amd/amdkfd/kfd_events.h | 2 ++
>>   2 files changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_events.c b/drivers/gpu/drm/amd/amdkfd/kfd_events.c
>> index 0fef24b0b915..75847c5d5957 100644
>> --- a/drivers/gpu/drm/amd/amdkfd/kfd_events.c
>> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_events.c
>> @@ -262,8 +262,7 @@ static void destroy_event(struct kfd_process *p, struct kfd_event *ev)
>>   		p->signal_event_count--;
>>   
>>   	idr_remove(&p->event_idr, ev->event_id);
>> -	synchronize_rcu();
>> -	kfree(ev);
>> +	kfree_rcu(ev, rcu);
>>   }
>>   
>>   static void destroy_events(struct kfd_process *p)
>> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_events.h b/drivers/gpu/drm/amd/amdkfd/kfd_events.h
>> index 55d376f56021..1c62c8dd6460 100644
>> --- a/drivers/gpu/drm/amd/amdkfd/kfd_events.h
>> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_events.h
>> @@ -70,6 +70,8 @@ struct kfd_event {
>>   		struct kfd_hsa_memory_exception_data memory_exception_data;
>>   		struct kfd_hsa_hw_exception_data hw_exception_data;
>>   	};
>> +
>> +	struct rcu_head rcu; /* for asynchronous kfree_rcu */
>>   };
>>   
>>   #define KFD_EVENT_TIMEOUT_IMMEDIATE 0