linux-kernel - Re: getaddrinfo slowdown in 3.17.1, due to getifaddrs

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Message-ID: <20141017062517.GA11584@casper.infradead.org>
Date:	Fri, 17 Oct 2014 07:25:17 +0100
From:	Thomas Graf <tgraf@...g.ch>
To:	"Steinar H. Gunderson" <sgunderson@...foot.com>
Cc:	linux-kernel@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>,
	Nikolay Aleksandrov <nikolay@...hat.com>
Subject: Re: getaddrinfo slowdown in 3.17.1, due to getifaddrs

On 10/17/14 at 02:34am, Steinar H. Gunderson wrote:
> On Fri, Oct 17, 2014 at 02:21:32AM +0200, Steinar H. Gunderson wrote:
> > Hi,
> > 
> > We recently upgraded a machine from 3.14.5 to 3.17.1, and a Perl script we're
> > running to poll SNMP suddenly needed ten times as much time to complete.
> 
> e341694e3eb57fcda9f1adc7bfea42fe080d8d7a looks like it might cause something
> like this (it certainly added the synchronize_net() call). Cc-ing people on 
> that commit; quoting the entire rest of the message for reference.

I think the only option at this point is to re-add the nltable lock to
netlink_lookup() so we can drop the synchronize_net() until we find a
way to RCUify socket destruction. I will cook up a patch today unless
somebody can come up with a smarter way to work around needing the
synchronize_net().
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