netdev - Re: [BUG]ethtool: NIC blink

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Message-ID: <1400596740.17377.50.camel@deadeye.wl.decadent.org.uk>
Date:	Tue, 20 May 2014 15:39:00 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Shawn Warren <shawn.warren@...kspace.com>
Cc:	netdev <netdev@...r.kernel.org>
Subject: Re: [BUG]ethtool: NIC blink

[Re-sending with cc to netdev]

On Tue, 2014-05-20 at 12:53 +0000, Shawn Warren wrote:
> Hello Ben and NetDev,
> 
> 
> I am curious how exactly the ethtool –p flag works when blinking
> interface lights. I ran into an issue on a DELL R820 with an Intel
> proc that when I blinked an interface and put ethtool in the
> background, the load on the server began steadily increasing. I ran
> the following command to reproduce the issue:
> 
> 
> # ethtool –p eth2 3600 &
> 
> 
> The load increased until the ethtool process was halted. Is this a
> known bug/issue?

It's not a bug in the ethtool utility.

Perhaps you have run into the problem explained in
<https://git.kernel.org/linus/68f512f21a64c9b264df6c61a9333e7890faf74b>.
The load will increase as processes wait (uninterruptibly) to obtain the
RTNL lock.  They will appear as being in D state.

This was fixed in Linux 3.0, but older versions can't practically be
fixed as it required an incompatible change to the driver API.

Ben.

-- 
Ben Hutchings
Life would be so much easier if we could look at the source code.

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