Re: [PATCH 2/3] io_uring: put flag checking for needing req cleanup in one spot

[Jens Axboe <axboe@kernel.dk>]

On 4/16/21 7:25 AM, Pavel Begunkov wrote:
> On 16/04/2021 02:25, Jens Axboe wrote:
>> We have this in two spots right now, which is a bit fragile. In
>> preparation for moving REQ_F_POLLED cleanup into the same spot, move
>> the check into io_clean_op() itself so we only have it once.
>>
>> Signed-off-by: Jens Axboe <axboe@kernel.dk>
>> ---
>>  fs/io_uring.c | 19 ++++++++-----------
>>  1 file changed, 8 insertions(+), 11 deletions(-)
>>
>> diff --git a/fs/io_uring.c b/fs/io_uring.c
>> index 87ce3dbcd4ca..a668d6a3319c 100644
>> --- a/fs/io_uring.c
>> +++ b/fs/io_uring.c
>> @@ -1601,8 +1601,7 @@ static void io_req_complete_post(struct io_kiocb *req, long res,
>>  static void io_req_complete_state(struct io_kiocb *req, long res,
>>  				  unsigned int cflags)
>>  {
>> -	if (req->flags & (REQ_F_NEED_CLEANUP | REQ_F_BUFFER_SELECTED))
>> -		io_clean_op(req);
>> +	io_clean_op(req);
>>  	req->result = res;
>>  	req->compl.cflags = cflags;
>>  	req->flags |= REQ_F_COMPLETE_INLINE;
>> @@ -1713,16 +1712,12 @@ static void io_dismantle_req(struct io_kiocb *req)
>>  
>>  	if (!(flags & REQ_F_FIXED_FILE))
>>  		io_put_file(req->file);
>> -	if (flags & (REQ_F_NEED_CLEANUP | REQ_F_BUFFER_SELECTED |
>> -		     REQ_F_INFLIGHT)) {
>> -		io_clean_op(req);
>> +	io_clean_op(req);
>> +	if (req->flags & REQ_F_INFLIGHT) {
>> +		struct io_uring_task *tctx = req->task->io_uring;
> 
> Not in particular happy about it.
> 1. adds extra if
> 2. adds extra function call
> 3. extra memory load in that function call.
> 
> Pushes us back in terms of performance. I'd suggest to have
> a helper, which is pretty much optimisable and may be coalesced by a compiler with
> adjacent flag checks.
> 
> static inline bool io_need_cleanup(unsigned flags)
> {
> 	return flags & (REQ_F_NEED_CLEANUP | REQ_F_BUFFER_SELECTED);
> }
> 
> if (io_need_cleanup(flags) || (flags & INFLIGHT)) {
>     io_clean_op();
>     if (INFLIGHT) {}
> }

Sure, we can do that. Particularly because of needing to rearrange
to get it inlined, but no big deal. I'll fiddle it.

-- 
Jens Axboe