netdev - Re: [PATCH v13 4/7] io-uring: add napi busy poll support

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Message-ID: <ZGdHGXOfbPd+i1qh@corigine.com>
Date: Fri, 19 May 2023 11:53:29 +0200
From: Simon Horman <simon.horman@...igine.com>
To: Stefan Roesch <shr@...kernel.io>
Cc: io-uring@...r.kernel.org, kernel-team@...com, axboe@...nel.dk,
	ammarfaizi2@...weeb.org, netdev@...r.kernel.org, kuba@...nel.org,
	olivier@...llion01.com
Subject: Re: [PATCH v13 4/7] io-uring: add napi busy poll support

On Thu, May 18, 2023 at 02:17:48PM -0700, Stefan Roesch wrote:
> This adds the napi busy polling support in io_uring.c. It adds a new
> napi_list to the io_ring_ctx structure. This list contains the list of
> napi_id's that are currently enabled for busy polling. The list is
> synchronized by the new napi_lock spin lock. The current default napi
> busy polling time is stored in napi_busy_poll_to. If napi busy polling
> is not enabled, the value is 0.
> 
> In addition there is also a hash table. The hash table store the napi
> id ond the pointer to the above list nodes. The hash table is used to

nit: is 'ond' correct here?

> speed up the lookup to the list elements. The hash table is synchronized
> with rcu.
> 
> The NAPI_TIMEOUT is stored as a timeout to make sure that the time a
> napi entry is stored in the napi list is limited.
> 
> The busy poll timeout is also stored as part of the io_wait_queue. This
> is necessary as for sq polling the poll interval needs to be adjusted
> and the napi callback allows only to pass in one value.
> 
> This has been tested with two simple programs from the liburing library
> repository: the napi client and the napi server program. The client
> sends a request, which has a timestamp in its payload and the server
> replies with the same payload. The client calculates the roundtrip time

nit: checkpatch.pl --codespell says:


:636: WARNING: 'calcualte' may be misspelled - perhaps 'calculate'?
and stores it to calcualte the results.
                 ^^^^^^^^^

...