netdev - Re: [PATCH RFC] IPv6: Avoid taking write lock for /proc/net/ipv6

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Message-ID: <CAKA=qzb=PYTMO=9KFpTJ9BVdDRkqbaCuW02pbW0onM8gU1E7sw@mail.gmail.com>
Date:	Sat, 31 Dec 2011 13:49:38 -0600
From:	Josh Hunt <joshhunt00@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	kuznet@....inr.ac.ru, jmorris@...ei.org, yoshfuji@...ux-ipv6.org,
	kaber@...sh.net, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] IPv6: Avoid taking write lock for /proc/net/ipv6_route

On Fri, Dec 30, 2011 at 4:09 PM, David Miller <davem@...emloft.net> wrote:
> From: Josh Hunt <joshhunt00@...il.com>
> Date: Wed, 28 Dec 2011 17:23:07 -0600
>
>> lock_stat shows taking the write lock is causing the slowdown. Using
>> this info I decided to write a version of fib6_clean_all() which
>> replaces write_lock_bh(&table->tb6_lock) with
>> read_lock_bh(&table->tb6_lock). With this new function I see the same
>> results as with my rtnetlink iperf test. I guess my question is what
>> am I missing? Is there a reason you need to take the write lock when
>> reading the route table to display to proc?
>
> You're not missing anything, it's just an oversight or laziness. :-)
>
> I've applied your patch thanks.
>
> Longer term we should make the ipv6 tree traversals RCU safe just
> like net/ipv4/fib_trie.c is.  Then we can do away with even the
> read locks for read-only traversals.
>

Thanks David. Are you aware if anyone has started the work to make
IPv6 traversals RCU safe?
-- 
Josh
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