public inbox for [email protected]
 help / color / mirror / Atom feed
From: Hao Xu <[email protected]>
To: Olivier Langlois <[email protected]>, Jens Axboe <[email protected]>
Cc: Pavel Begunkov <[email protected]>,
	io-uring <[email protected]>,
	linux-kernel <[email protected]>
Subject: Re: [PATCH v1] io_uring: Add support for napi_busy_poll
Date: Tue, 1 Mar 2022 16:23:00 +0800	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>


On 3/1/22 05:01, Olivier Langlois wrote:
> On Tue, 2022-03-01 at 02:26 +0800, Hao Xu wrote:
>> On 2/25/22 13:32, Olivier Langlois wrote:
>>> On Mon, 2022-02-21 at 13:23 +0800, Hao Xu wrote:
>>>>> @@ -5776,6 +5887,7 @@ static int __io_arm_poll_handler(struct
>>>>> io_kiocb *req,
>>>>>                   __io_poll_execute(req, mask);
>>>>>                   return 0;
>>>>>           }
>>>>> +       io_add_napi(req->file, req->ctx);
>>>> I think this may not be the right place to do it. the process
>>>> will
>>>> be:
>>>> arm_poll sockfdA--> get invalid napi_id from sk->napi_id -->
>>>> event
>>>> triggered --> arm_poll for sockfdA again --> get valid napi_id
>>>> then why not do io_add_napi() in event
>>>> handler(apoll_task_func/poll_task_func).
>>> You have a valid concern that the first time a socket is passed to
>>> io_uring that napi_id might not be assigned yet.
>>>
>>> OTOH, getting it after data is available for reading does not help
>>> neither since busy polling must be done before data is received.
>>>
>>> for both places, the extracted napi_id will only be leveraged at
>>> the
>>> next polling.
>> Hi Olivier,
>>
>> I think we have some gap here. AFAIK, it's not 'might not', it is
>>
>> 'definitely not', the sk->napi_id won't be valid until the poll
>> callback.
>>
>> Some driver's code FYR:
>> (drivers/net/ethernet/intel/e1000/e1000_main.c)
>>
>> e1000_receive_skb-->napi_gro_receive-->napi_skb_finish--
>>> gro_normal_one
>> and in gro_normal_one(), it does:
>>
>>             if (napi->rx_count >= gro_normal_batch)
>>                     gro_normal_list(napi);
>>
>>
>> The gro_normal_list() delivers the info up to the specifical network
>> protocol like tcp.
>>
>> And then sk->napi_id is set, meanwhile the poll callback is
>> triggered.
>>
>> So that's why I call the napi polling technology a 'speculation'.
>> It's
>> totally for the
>>
>> future data. Correct me if I'm wrong especially for the poll callback
>> triggering part.
>>
> When I said 'might not', I was meaning that from the io_uring point of
> view, it has no idea what is the previous socket usage. If it has been
> used outside io_uring, the napi_id could available on the first call.
>
> If it is really read virgin socket, neither my choosen call site or
> your proposed sites will make the napi busy poll possible for the first
> poll.
>
> I feel like there is not much to gain to argue on this point since I
> pretty much admitted that your solution was most likely the only call
> site making MULTIPOLL requests work correctly with napi busy poll as
> those requests could visit __io_arm_poll_handler only once (Correct me
> if my statement is wrong).
>
> The only issue was that I wasn't sure is how using your calling sites
> would make locking work.
>
> I suppose that adding a dedicated spinlock for protecting napi_list
> instead of relying on uring_lock could be a solution. Would that work?
spinlock should be fine.

      reply	other threads:[~2022-03-01  8:23 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-02-19  8:03 [PATCH v1] io_uring: Add support for napi_busy_poll Olivier Langlois
2022-02-19 21:42 ` Olivier Langlois
2022-02-20  0:22   ` Jens Axboe
2022-02-20 18:37     ` Olivier Langlois
2022-02-20 19:38       ` Jens Axboe
2022-02-21 19:29         ` Olivier Langlois
2022-02-21  5:25       ` Hao Xu
2022-02-20 20:51 ` kernel test robot
2022-02-20 21:53 ` kernel test robot
2022-02-20 21:53 ` kernel test robot
2022-02-21  5:23 ` Hao Xu
2022-02-25  5:32   ` Olivier Langlois
2022-02-25 15:32     ` Olivier Langlois
2022-02-28 18:34       ` Hao Xu
2022-02-28 21:20         ` Olivier Langlois
2022-03-01  3:53           ` Hao Xu
2022-02-28 18:26     ` Hao Xu
2022-02-28 21:01       ` Olivier Langlois
2022-03-01  8:23         ` Hao Xu [this message]

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=7695c3a2-6cb0-067a-5655-0e6180170bde@linux.alibaba.com \
    [email protected] \
    [email protected] \
    [email protected] \
    [email protected] \
    [email protected] \
    [email protected] \
    /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
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox