netdev - Re: IFLA_INET6

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Date:	Wed, 09 Sep 2015 16:00:58 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Sowmini Varadhan <sowmini.varadhan@...cle.com>
Cc:	netdev@...r.kernel.org, raghavendra.kt@...ux.vnet.ibm.com
Subject: Re: IFLA_INET6_[ICMP6]STATS

On Wed, 2015-09-09 at 17:34 -0400, Sowmini Varadhan wrote:
> I'm doing some experiments that are trying to simultaneously
> scaling the number of CPUs, and the number of processes 
> and encountering getifaddrs() weaknesses.
> 
> Others have run into similar things in the past,  e.g., 
>   http://lists.openwall.net/netdev/2014/01/23/119
> and more relevant to my experiment: the findings behind 
> the recent commit a3a77372.
> 
> In my case, it looks like getifaddrs() doesnt even use the
> results of IFLA_INET6_STATS or IFLA_INET6_ICMP6STATS- 
> from my scan of glibc, this information is ignored (it only 
> looks at IFLA_STATS).  Moreover, if I hack out  all of 
> snmp_fold_field() (so that it always returns 0),  it helps 
> my cpu utilization and scaling, and no errors are reported.
> 
> So the question is- who uses IFLA_INET6_STATS/IFLA_INET6_ICMP6STATS?
> Is this intended for some ND/ripngd etc daemon?  Doesnt seem to 
> be documented in rtnetlink(7), and couldnt find any users in glibc,
> and google did not find any usage. 

At least ICMP6 stats do not have O(Ncpu) cost anymore,
after commit be281e554e2a4cf2478df7a8b8926c89454bccfa
("ipv6: reduce per device ICMP mib sizes")



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