netdev - Re: [PATCH net-next] ip6mr: remove synchronize_rcu() in favor of SOCK_RCU

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Message-Id: <20180307.181418.1356901556042128422.davem@davemloft.net>
Date:   Wed, 07 Mar 2018 18:14:18 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     eric.dumazet@...il.com
Cc:     yuvalm@...lanox.com, ktkhai@...tuozzo.com, yoshfuji@...ux-ipv6.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH net-next] ip6mr: remove synchronize_rcu() in favor of
 SOCK_RCU_FREE

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Wed, 07 Mar 2018 08:43:19 -0800

> From: Eric Dumazet <edumazet@...gle.com>
> 
> Kirill found that recently added synchronize_rcu() call in
> ip6mr_sk_done()
> was slowing down netns dismantle and posted a patch to use it only if
> the socket
> was found.
> 
> I instead suggested to get rid of this call, and use instead
> SOCK_RCU_FREE
> 
> We might later change IPv4 side to use the same technique and unify
> both stacks. IPv4 does not use synchronize_rcu() but has a call_rcu()
> that could be replaced by SOCK_RCU_FREE.
> 
> Tested:
>  time for i in {1..1000}; do unshare -n /bin/false;done
> 
>  Before : real 7m18.911s
>  After : real 10.187s
> 
> Fixes: 8571ab479a6e ("ip6mr: Make mroute_sk rcu-based")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: Kirill Tkhai <ktkhai@...tuozzo.com>
> Cc: Yuval Mintz <yuvalm@...lanox.com>

Looks great, applied, thanks everyone.