Re: [PATCH 4/4] io_uring: mark opcodes that always need io-wq punt

[Jens Axboe <axboe@kernel.dk>]

On 4/24/23 8:13?PM, Ming Lei wrote:
> On Mon, Apr 24, 2023 at 08:08:09PM -0600, Jens Axboe wrote:
>> On 4/24/23 6:57?PM, Ming Lei wrote:
>>> On Mon, Apr 24, 2023 at 09:24:33AM -0600, Jens Axboe wrote:
>>>> On 4/24/23 1:30?AM, Ming Lei wrote:
>>>>> On Thu, Apr 20, 2023 at 12:31:35PM -0600, Jens Axboe wrote:
>>>>>> Add an opdef bit for them, and set it for the opcodes where we always
>>>>>> need io-wq punt. With that done, exclude them from the file_can_poll()
>>>>>> check in terms of whether or not we need to punt them if any of the
>>>>>> NO_OFFLOAD flags are set.
>>>>>>
>>>>>> Signed-off-by: Jens Axboe <axboe@kernel.dk>
>>>>>> ---
>>>>>>  io_uring/io_uring.c |  2 +-
>>>>>>  io_uring/opdef.c    | 22 ++++++++++++++++++++--
>>>>>>  io_uring/opdef.h    |  2 ++
>>>>>>  3 files changed, 23 insertions(+), 3 deletions(-)
>>>>>>
>>>>>> diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
>>>>>> index fee3e461e149..420cfd35ebc6 100644
>>>>>> --- a/io_uring/io_uring.c
>>>>>> +++ b/io_uring/io_uring.c
>>>>>> @@ -1948,7 +1948,7 @@ static int io_issue_sqe(struct io_kiocb *req, unsigned int issue_flags)
>>>>>>  		return -EBADF;
>>>>>>  
>>>>>>  	if (issue_flags & IO_URING_F_NO_OFFLOAD &&
>>>>>> -	    (!req->file || !file_can_poll(req->file)))
>>>>>> +	    (!req->file || !file_can_poll(req->file) || def->always_iowq))
>>>>>>  		issue_flags &= ~IO_URING_F_NONBLOCK;
>>>>>
>>>>> I guess the check should be !def->always_iowq?
>>>>
>>>> How so? Nobody that takes pollable files should/is setting
>>>> ->always_iowq. If we can poll the file, we should not force inline
>>>> submission. Basically the ones setting ->always_iowq always do -EAGAIN
>>>> returns if nonblock == true.
>>>
>>> I meant IO_URING_F_NONBLOCK is cleared here for  ->always_iowq, and
>>> these OPs won't return -EAGAIN, then run in the current task context
>>> directly.
>>
>> Right, of IO_URING_F_NO_OFFLOAD is set, which is entirely the point of
>> it :-)
> 
> But ->always_iowq isn't actually _always_ since fallocate/fsync/... are
> not punted to iowq in case of IO_URING_F_NO_OFFLOAD, looks the naming of
> ->always_iowq is a bit confusing?

Yeah naming isn't that great, I can see how that's bit confusing. I'll
be happy to take suggestions on what would make it clearer.

-- 
Jens Axboe