netdev - Re: [RFC PATCH v2] netpoll: Remove 4s sleep during carrier detection

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Date:   Thu, 19 Jan 2023 11:04:21 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Breno Leitao <leitao@...ian.org>
Cc:     netdev@...r.kernel.org, leit@...com, davem@...emloft.net,
        edumazet@...gle.com, pabeni@...hat.com,
        sa+renesas@...g-engineering.com, linux-kernel@...r.kernel.org,
        Michael van der Westhuizen <rmikey@...a.com>
Subject: Re: [RFC PATCH v2] netpoll: Remove 4s sleep during carrier
 detection

On Thu, 19 Jan 2023 10:00:08 -0800 Breno Leitao wrote:
> This patch proposes to remove the msleep(4s) during netpoll_setup() if
> the carrier appears instantly.
> 
> Modern NICs do not seem to have this bouncing problem anymore, and this
> sleep slows down the machine boot unnecessarily

We should mention in the message that the wait is counter-productive on
servers which have BMC communicating over NC-SI via the same NIC as gets
used for netconsole. BMC will keep the PHY up, hence the carrier
appearing instantly.

We could add a smaller delay, but really having instant carrier and
then loosing it seems like a driver bug, so let's try to rip the band
aid off and ask for forgiveness instead.

Few extra process rules:
 - don't repost another version within 24h,
 - keep a changelog under --- 
 - add tree name to the tag - [PATCH net-next]

Also, I'd just go for PATCH, no need to RFC this.
If someone wants to object they can object to a PATCH.