[PATCH] io_uring: add EPOLLEXCLUSIVE flag to aoid thundering herd type behavior

[PATCH] io_uring: add EPOLLEXCLUSIVE flag to aoid thundering herd type behavior

[Jiufei Xue]

Applications can use this flag to avoid accept thundering herd.

Signed-off-by: Jiufei Xue <jiufei.xue@linux.alibaba.com>
---
 fs/io_uring.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index f668982..b8102b2 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -4109,7 +4109,10 @@ static void __io_queue_proc(struct io_poll_iocb *poll, struct io_poll_table *pt,
 
 	pt->error = 0;
 	poll->head = head;
-	add_wait_queue(head, &poll->wait);
+	if (poll->events & EPOLLEXCLUSIVE)
+		add_wait_queue_exclusive(head, &poll->wait);
+	else
+		add_wait_queue(head, &poll->wait);
 }
 
 static void io_async_queue_proc(struct file *file, struct wait_queue_head *head,
@@ -4530,7 +4533,7 @@ static int io_poll_add_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe
 		return -EBADF;
 
 	events = READ_ONCE(sqe->poll_events);
-	poll->events = demangle_poll(events) | EPOLLERR | EPOLLHUP;
+	poll->events = demangle_poll(events) | EPOLLERR | EPOLLHUP | EPOLLEXCLUSIVE;
 
 	get_task_struct(current);
 	req->task = current;
-- 
1.8.3.1

Re: [PATCH] io_uring: add EPOLLEXCLUSIVE flag to aoid thundering herd type behavior

[Jens Axboe]

On 6/10/20 12:15 AM, Jiufei Xue wrote:
> Applications can use this flag to avoid accept thundering herd.

So with this, any IORING_OP_POLL_ADD will be exclusive. Seems to me
that the other poll path we have could use it too by default, and
at that point, we could clean this up (and improve) it further by
including that?

-- 
Jens Axboe

Re: [PATCH] io_uring: add EPOLLEXCLUSIVE flag to aoid thundering herd type behavior

[Jiufei Xue]

On 2020/6/11 上午8:01, Jens Axboe wrote:
> On 6/10/20 12:15 AM, Jiufei Xue wrote:
>> Applications can use this flag to avoid accept thundering herd.
> 
> So with this, any IORING_OP_POLL_ADD will be exclusive. Seems to me
> that the other poll path we have could use it too by default, and
> at that point, we could clean this up (and improve) it further by
> including that?
> 
Sorry, I have sent the wrong patch. I think the flag should be determined by
user, I will send the new version soon.

Thanks,
JIufei.

Re: [PATCH] io_uring: add EPOLLEXCLUSIVE flag to aoid thundering herd type behavior

[Jens Axboe]

On 6/10/20 7:36 PM, Jiufei Xue wrote:
> 
> 
> On 2020/6/11 上午8:01, Jens Axboe wrote:
>> On 6/10/20 12:15 AM, Jiufei Xue wrote:
>>> Applications can use this flag to avoid accept thundering herd.
>>
>> So with this, any IORING_OP_POLL_ADD will be exclusive. Seems to me
>> that the other poll path we have could use it too by default, and
>> at that point, we could clean this up (and improve) it further by
>> including that?
>>
> Sorry, I have sent the wrong patch. I think the flag should be determined by
> user, I will send the new version soon.

That's sort of what I assumed as well.

-- 
Jens Axboe