Re: 答复: [PATCH for-next] io_uring: ensure io_queue_deferred() is out-of-line

[Jens Axboe <axboe@kernel.dk>]

On 1/2/25 5:38 AM, lizetao wrote:
> Hi,
> 
>> -----Original Message-----
>> From: Jens Axboe <axboe@kernel.dk>
>> Sent: Tuesday, December 31, 2024 8:37 AM
>> To: io-uring <io-uring@vger.kernel.org>
>> Subject: [PATCH for-next] io_uring: ensure io_queue_deferred() is out-of-line
>>
>> This is not the hot path, it's a slow path. Yet the locking for it is in the hot path,
>> and __cold does not prevent it from being inlined.
>>
>> Move the locking to the function itself, and mark it noinline as well to avoid it
>> polluting the icache of the hot path.
>>
>> Signed-off-by: Jens Axboe <axboe@kernel.dk>
>>
>> ---
>>
>> diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c index
>> 42d4cc5da73b..db198bd435b5 100644
>> --- a/io_uring/io_uring.c
>> +++ b/io_uring/io_uring.c
>> @@ -550,8 +550,9 @@ void io_req_queue_iowq(struct io_kiocb *req)
>>  	io_req_task_work_add(req);
>>  }
>>
>> -static __cold void io_queue_deferred(struct io_ring_ctx *ctx)
>> +static __cold noinline void io_queue_deferred(struct io_ring_ctx *ctx)
>>  {
>> +	spin_lock(&ctx->completion_lock);
> Just a digression, whether the io_uring subsystem welcomes scope-based
> cleanup helpers, this is somewhat

We welcome any change that makes sense :-)

For this particular one, no point having io_queue_deferred() marked as
cold yet still inlined, and no point having the locking outside of the
helper as that gets inlined as well.

-- 
Jens Axboe