netdev - Re: v6: faster tree-based sysctl implementation

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Date:	Tue, 6 Dec 2011 16:33:10 +0200
From:	Lucian Adrian Grijincu <lucian.grijincu@...il.com>
To:	Anca Emanuel <anca.emanuel@...il.com>
Cc:	"Eric W . Biederman" <ebiederm@...ssion.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	netdev@...r.kernel.org, Octavian Purdila <tavi@...pub.ro>,
	"David S . Miller" <davem@...emloft.net>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Damien Millescamps <damien.millescamps@...nd.com>
Subject: Re: v6: faster tree-based sysctl implementation

On Tue, Dec 6, 2011 at 4:11 PM, Anca Emanuel <anca.emanuel@...il.com> wrote:
> time modprobe dummy numdummies=1000FATAL: Error inserting dummy
> (/lib/modules/3.2.0-3-generic/kernel/drivers/net/dummy.ko): Operation
> not permitted

Generally when you get "Operation not permitted" you should try with sudo.
This is the man-page: http://xkcd.com/149/ :)

> What are the practical problems you solve with this ?
> Name one or more.

Sysctl uses a slow algorithm: O(N^2) for insertions, O(N) for lookup,
with a relatively big constant.
The performance is acceptable when N is small, but sometimes it can
grow to bigger values.
One case where N can grow to very large values is when you add network
interfaces.

Some companies (like IXIACOM which sponsored this work at the
beginning of this year) have use-cases in which they need 10^3..10^6
network interfaces. The current sysctl implementation is unacceptable
for them.

@Damien Millescamps might have some input on where he needs better
sysctl performance as he prompted me to re-send this patch series.

This algorithm is O(N * logN) for insert and O(logN) for lookup.

> You add more code. This is not good. If you reduce the code, then it
> will be interesting.

Thank you. I know that, but it's easier said than done. I'd welcome
some feedback in what could be simplified in my patches :)

-- 
 .
..: Lucian
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