netdev - Re: [PATCH ethtool] ethtool: Add support for 200Gbps (50Gbps per lane) link mode

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Message-ID: <20190224204336.GC20855@lunn.ch>
Date:   Sun, 24 Feb 2019 21:43:36 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Michal Kubecek <mkubecek@...e.cz>
Cc:     Tariq Toukan <tariqt@...lanox.com>,
        "John W. Linville" <linville@...driver.com>,
        netdev@...r.kernel.org, Eran Ben Elisha <eranbe@...lanox.com>,
        Aya Levin <ayal@...lanox.com>
Subject: Re: [PATCH ethtool] ethtool: Add support for 200Gbps (50Gbps per
 lane) link mode

> > Hi Michal
> > 
> > So are you doing a read/modify/write? In that case, off/on makes
> > sense. For a pure write, i don't see the need for off/on.
> 
> When using netlink interface, the read/modify/write cycle is limited to
> kernel code and is done under rtnl_lock. The netlink interface allows
> userspace to send only attributes it wants to change and for bit sets
> (like link modes) to tell kernel which bits it wants to change so that
> there is no need to read current values first (and open a race window).

Nice.

But it would still be good to get feedback from people who use this
more often. I guess that is top of rack switches with all these odd
link modes.

     Andrew