IO-Uring Archive on lore.kernel.org
 help / color / Atom feed
From: Jens Axboe <axboe@kernel.dk>
To: Stefano Garzarella <sgarzare@redhat.com>
Cc: linux-kernel@vger.kernel.org, io-uring@vger.kernel.org
Subject: Re: [PATCH liburing v2 0/1] test: add epoll test case
Date: Thu, 6 Feb 2020 12:15:49 -0700
Message-ID: <ec04cb8f-01e8-6289-2fd4-6dec8a8e2c02@kernel.dk> (raw)
In-Reply-To: <CAGxU2F6qvW28=ULNUi-UHethus2bO6VXYX127HOcH_KPToZC-w@mail.gmail.com>

On 2/6/20 10:33 AM, Stefano Garzarella wrote:
> 
> 
> On Fri, Jan 31, 2020 at 4:39 PM Jens Axboe <axboe@kernel.dk> wrote:
>>
>> On 1/31/20 7:29 AM, Stefano Garzarella wrote:
>>> Hi Jens,
>>> this is a v2 of the epoll test.
>>>
>>> v1 -> v2:
>>>     - if IORING_FEAT_NODROP is not available, avoid to overflow the CQ
>>>     - add 2 new tests to test epoll with IORING_FEAT_NODROP
>>>     - cleanups
>>>
>>> There are 4 sub-tests:
>>>     1. test_epoll
>>>     2. test_epoll_sqpoll
>>>     3. test_epoll_nodrop
>>>     4. test_epoll_sqpoll_nodrop
>>>
>>> In the first 2 tests, I try to avoid to queue more requests than we have room
>>> for in the CQ ring. These work fine, I have no faults.
>>
>> Thanks!
>>
>>> In the tests 3 and 4, if IORING_FEAT_NODROP is supported, I try to submit as
>>> much as I can until I get a -EBUSY, but they often fail in this way:
>>> the submitter manages to submit everything, the receiver receives all the
>>> submitted bytes, but the cleaner loses completion events (I also tried to put a
>>> timeout to epoll_wait() in the cleaner to be sure that it is not related to the
>>> patch that I send some weeks ago, but the situation doesn't change, it's like
>>> there is still overflow in the CQ).
>>>
>>> Next week I'll try to investigate better which is the problem.
>>
>> Does it change if you have an io_uring_enter() with GETEVENTS set? I wonder if
>> you just pruned the CQ ring but didn't flush the internal side.
> 
> If I do io_uring_enter() with GETEVENTS set and wait_nr = 0 it solves
> the issue, I think because we call io_cqring_events() that flushes the
> overflow list.
> 
> At this point, should we call io_cqring_events() (that flushes the
> overflow list) in io_uring_poll()?
> I mean something like this:
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 77f22c3da30f..2769451af89a 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -6301,7 +6301,7 @@ static __poll_t io_uring_poll(struct file *file, poll_table *wait)
>         if (READ_ONCE(ctx->rings->sq.tail) - ctx->cached_sq_head !=
>             ctx->rings->sq_ring_entries)
>                 mask |= EPOLLOUT | EPOLLWRNORM;
> -       if (READ_ONCE(ctx->rings->cq.head) != ctx->cached_cq_tail)
> +       if (!io_cqring_events(ctx, false))
>                 mask |= EPOLLIN | EPOLLRDNORM;
> 
>         return mask;

That's not a bad idea, would just have to verify that it is indeed safe
to always call the flushing variant from there.

-- 
Jens Axboe


  reply index

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-31 14:29 Stefano Garzarella
2020-01-31 14:29 ` [PATCH liburing v2 1/1] " Stefano Garzarella
2020-01-31 15:41   ` Jens Axboe
2020-02-03  9:04     ` Stefano Garzarella
2020-02-03 15:43       ` Jens Axboe
2020-01-31 15:39 ` [PATCH liburing v2 0/1] " Jens Axboe
2020-02-03  9:03   ` Stefano Garzarella
2020-02-06 17:33   ` Stefano Garzarella
2020-02-06 19:15     ` Jens Axboe [this message]
2020-02-06 19:51       ` Jens Axboe
2020-02-06 20:12         ` Stefano Garzarella
2020-02-06 19:46     ` Jens Axboe
2020-02-07 16:51   ` Stefano Garzarella

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=ec04cb8f-01e8-6289-2fd4-6dec8a8e2c02@kernel.dk \
    --to=axboe@kernel.dk \
    --cc=io-uring@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=sgarzare@redhat.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

IO-Uring Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/io-uring/0 io-uring/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 io-uring io-uring/ https://lore.kernel.org/io-uring \
		io-uring@vger.kernel.org
	public-inbox-index io-uring

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.io-uring


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git