Re: [dpdk-dev] [PATCH] eal/ipc: stop async IPC loop on callback request

["Burakov, Anatoly" <anatoly.burakov@intel.com>]

On 10-Apr-18 2:53 PM, Tan, Jianfeng wrote:
> 
> 
> On 4/10/2018 6:03 PM, Anatoly Burakov wrote:
>> EAL did not stop processing further asynchronous requests on
>> encountering a request that should trigger the callback. This
>> resulted in erasing valid requests but not triggering them.
> 
> That means one wakeup could process multiple replies, and following 
> process_async_request() will erase some valid requests?

Yes.

> 
>>
>> Fix this by stopping the loop once we have a request that we
>> can trigger. Also, remove unnecessary check for trigger
>> request being NULL.
>>
>> Fixes: f05e26051c15 ("eal: add IPC asynchronous request")
>> Cc: anatoly.burakov@intel.com
>>
>> Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>
> 
> 
>> ---
>>   lib/librte_eal/common/eal_common_proc.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/lib/librte_eal/common/eal_common_proc.c 
>> b/lib/librte_eal/common/eal_common_proc.c
>> index f98622f..1ea3b58 100644
>> --- a/lib/librte_eal/common/eal_common_proc.c
>> +++ b/lib/librte_eal/common/eal_common_proc.c
>> @@ -510,11 +510,11 @@ async_reply_handle(void *arg __rte_unused)
>>                       TAILQ_REMOVE(&pending_requests.requests,
>>                               sr, next);
>>                       free(sr);
>> -                } else if (action == ACTION_TRIGGER &&
>> -                        trigger == NULL) {
>> +                } else if (action == ACTION_TRIGGER) {
>>                       TAILQ_REMOVE(&pending_requests.requests,
>>                               sr, next);
>>                       trigger = sr;
>> +                    break;
> 
> If I understand it correctly above, break here, we will trigger an async 
> action, and then go back to sleep with some ready requests not handled? 
> Seems that we shall unlock, process, and lock here. Right?

Well, we won't go back to sleep - we'll just loop around and come back.

See eal_common_proc.c:472:

	/* sometimes, we don't even wait */
	if (sr->reply_received) {
		nowait = true;
		break;
	}

Followed by line 478:

	if (nowait)
		ret = 0;

Followed by line 495:

	if (ret == 0 || ret == ETIMEDOUT) {

So, having messages with replies already in the queue will cause wait to 
be cancelled. It's not much slower than unlocking, triggering, and 
locking again.

However, if you're OK with lock-loop-unlock-trigger-lock-loop-unlock-... 
sequence until we run out of triggers, then sure, i can add that.

> 
> Thanks,
> Jianfeng
> 
>>                   }
>>               }
>>           }
> 
> 


-- 
Thanks,
Anatoly