From:   David Laight <David.Laight@ACULAB.COM>
To:     'Breno Leitao' <leitao@debian.org>,
        "kuba@kernel.org" <kuba@kernel.org>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>
CC:     "leit@fb.com" <leit@fb.com>,
        "davem@davemloft.net" <davem@davemloft.net>,
        "edumazet@google.com" <edumazet@google.com>,
        "pabeni@redhat.com" <pabeni@redhat.com>,
        "andrew@lunn.ch" <andrew@lunn.ch>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "Michael van der Westhuizen" <rmikey@meta.com>
Subject: RE: [PATCH v3] netpoll: Remove 4s sleep during carrier detection
Thread-Topic: [PATCH v3] netpoll: Remove 4s sleep during carrier detection
Thread-Index: AQHZMO474M9dVibggUerw/Y/8Leyua6wZmjA
Date:   Thu, 26 Jan 2023 09:04:42 +0000
Message-ID: <6d13242627e84bde8129e75b6324d905@AcuMS.aculab.com>
References: <20230125185230.3574681-1-leitao@debian.org>
In-Reply-To: <20230125185230.3574681-1-leitao@debian.org>
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From: Breno Leitao
> Sent: 25 January 2023 18:53
> This patch removes the msleep(4s) during netpoll_setup() if the carrier
> appears instantly.
> 
> Here are some scenarios where this workaround is counter-productive in
> modern ages:
> 
> 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.
> 
> The link is fibre, SERDES getting sync could happen within 0.1Hz, and
> the carrier also appears instantly.
> 
> Other than that, if a driver is reporting instant carrier and then
> losing it, this is probably a driver bug.

I can't help feeling that this will break something.
The 4 second delay does look counter productive though.
Obvious alternatives are 'wait a bit before the first check'
and 'require carrier to be present for a few checks'.

It also has to be said that checking every ms seems over enthusiastic.

	David

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