Re: [PATCH] io_uring/uring_cmd: push IRQ based completions through task_work

[Jens Axboe <axboe@kernel.dk>]

On 3/20/23 5:35?PM, Ming Lei wrote:
> On Mon, Mar 20, 2023 at 08:36:15PM +0530, Kanchan Joshi wrote:
>> On Sun, Mar 19, 2023 at 8:51?PM Jens Axboe <axboe@kernel.dk> wrote:
>>>
>>> This is similar to what we do on the non-passthrough read/write side,
>>> and helps take advantage of the completion batching we can do when we
>>> post CQEs via task_work. On top of that, this avoids a uring_lock
>>> grab/drop for every completion.
>>>
>>> In the normal peak IRQ based testing, this increases performance in
>>> my testing from ~75M to ~77M IOPS, or an increase of 2-3%.
>>>
>>> Signed-off-by: Jens Axboe <axboe@kernel.dk>
>>>
>>> ---
>>>
>>> diff --git a/io_uring/uring_cmd.c b/io_uring/uring_cmd.c
>>> index 2e4c483075d3..b4fba5f0ab0d 100644
>>> --- a/io_uring/uring_cmd.c
>>> +++ b/io_uring/uring_cmd.c
>>> @@ -45,18 +45,21 @@ static inline void io_req_set_cqe32_extra(struct io_kiocb *req,
>>>  void io_uring_cmd_done(struct io_uring_cmd *ioucmd, ssize_t ret, ssize_t res2)
>>>  {
>>>         struct io_kiocb *req = cmd_to_io_kiocb(ioucmd);
>>> +       struct io_ring_ctx *ctx = req->ctx;
>>>
>>>         if (ret < 0)
>>>                 req_set_fail(req);
>>>
>>>         io_req_set_res(req, ret, 0);
>>> -       if (req->ctx->flags & IORING_SETUP_CQE32)
>>> +       if (ctx->flags & IORING_SETUP_CQE32)
>>>                 io_req_set_cqe32_extra(req, res2, 0);
>>> -       if (req->ctx->flags & IORING_SETUP_IOPOLL)
>>> +       if (ctx->flags & IORING_SETUP_IOPOLL) {
>>>                 /* order with io_iopoll_req_issued() checking ->iopoll_complete */
>>>                 smp_store_release(&req->iopoll_completed, 1);
>>> -       else
>>> -               io_req_complete_post(req, 0);
>>> +               return;
>>> +       }
>>> +       req->io_task_work.func = io_req_task_complete;
>>> +       io_req_task_work_add(req);
>>>  }
>>
>> Since io_uring_cmd_done itself would be executing in task-work often
>> (always in case of nvme), can this be further optimized by doing
>> directly what this new task-work (that is being set up here) would
>> have done?
>> Something like below on top of your patch -
> 
> But we have io_uring_cmd_complete_in_task() already, just wondering why
> not let driver decide if explicit running in task-work is taken?

Because it's currently broken, see my patch from earlier today.

-- 
Jens Axboe