netdev - Re: [RFC PATCH v3 0/3] io_uring: add napi busy polling support

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Message-ID: <44c2f431-6fd0-13c7-7b53-59237e24380a@kernel.dk>
Date:   Wed, 16 Nov 2022 11:44:38 -0700
From:   Jens Axboe <axboe@...nel.dk>
To:     Jakub Kicinski <kuba@...nel.org>, Stefan Roesch <shr@...kernel.io>
Cc:     kernel-team@...com, olivier@...llion01.com, netdev@...r.kernel.org,
        io-uring@...r.kernel.org
Subject: Re: [RFC PATCH v3 0/3] io_uring: add napi busy polling support

On 11/16/22 11:31 AM, Jakub Kicinski wrote:
> On Mon, 14 Nov 2022 23:08:57 -0800 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. This list is
>> used to determine which napi id's enabled busy polling.
>>
>> To set the new napi busy poll timeout, a new io-uring api has been
>> added. It sets the napi busy poll timeout for the corresponding ring.
>>
>> There is also a corresponding liburing patch series, which enables this
>> feature. The name of the series is "liburing: add add api for napi busy
>> poll timeout". It also contains two programs to test the this.
>>
>> Testing has shown that the round-trip times are reduced to 38us from
>> 55us by enabling napi busy polling with a busy poll timeout of 100us.
> 
> Acked-by: Jakub Kicinski <kuba@...nel.org>
> 
> Thanks!

Thanks Jakub! Question on the need for patch 3, which I think came about
because of comments from you. Can you expand on why we need both an
enable and timeout setting? Are there cases where timeout == 0 and
enabled == true make sense?

-- 
Jens Axboe