netdev - Re: Network cooling device and how to control NIC speed on thermal condition

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Message-ID: <20170508140225.GD19995@lunn.ch>
Date:   Mon, 8 May 2017 16:02:25 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Waldemar Rymarkiewicz <waldemar.rymarkiewicz@...il.com>
Cc:     Alan Cox <gnomes@...rguk.ukuu.org.uk>,
        Florian Fainelli <f.fainelli@...il.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Network cooling device and how to control NIC speed on thermal
 condition

> However, the fact is that PHYs having active 1G/s link generate much
> more heat than having 100M/s link independently from network traffic.

Yes, this is true. I got an off-list email suggesting this power
difference is very significant, more so than actually processing
packets.

> All cooling methods impact host only, but "net cooling" impacts remote
> side in addition, which seems to me to be a problem sometimes. Also,
> the moment of link renegotiation blocks rx/tx for upper layers, so the
> user sees a pause when streaming a video for example. However, if a
> system is under a thermal condition, does it really matter?

I don't know the cooling subsystem too well. Can you express a 'cost'
for making a change, as well as the likely result in making the
change. You might want to make the cost high, so it is used as a last
resort if other methods cannot give enough cooling.

       Andrew