Re: [PATCH for-next v2 11/12] io_uring: do msg_ring in target task via tw

[Pavel Begunkov <asml.silence@gmail.com>]

On 12/7/22 15:51, Jens Axboe wrote:
> On 12/7/22 8:31 AM, Jens Axboe wrote:
>> On 12/6/22 8:53?PM, Pavel Begunkov wrote:
>>> @@ -43,6 +61,15 @@ static int io_msg_ring_data(struct io_kiocb *req)
>>>   	if (msg->src_fd || msg->dst_fd || msg->flags)
>>>   		return -EINVAL;
>>>   
>>> +	if (target_ctx->task_complete && current != target_ctx->submitter_task) {
>>> +		init_task_work(&msg->tw, io_msg_tw_complete);
>>> +		if (task_work_add(target_ctx->submitter_task, &msg->tw,
>>> +				  TWA_SIGNAL))
>>> +			return -EOWNERDEAD;
>>> +
>>> +		return IOU_ISSUE_SKIP_COMPLETE;
>>> +	}
>>> +
>>
>> We should probably be able to get by with TWA_SIGNAL_NO_IPI here, no?
> 
> Considering we didn't even wake before, I'd say that's a solid yes.

I'm not so sure. It'll work, but a naive approach would also lack
IORING_SETUP_TASKRUN_FLAG and so mess with latencies when it's not
desirable.

option 1)

method = TWA_SIGNAL;
if (flags & IORING_SETUP_TASKRUN_FLAG)
	method = NO_IPI;

option 2)

task_work_add(NO_IPI);
atomic_or(IORING_SQ_TASKRUN, &ctx->rings->sq_flags);


Might be better to have one of those.

-- 
Pavel Begunkov