netdev - Re: [PATCH net-next V2] net ipv6: convert fib6

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Message-ID: <1501866461.25002.41.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Fri, 04 Aug 2017 10:07:41 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Shaohua Li <shli@...nel.org>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, Kernel-team@...com,
        Shaohua Li <shli@...com>, Wei Wang <weiwan@...gle.com>,
        Stephen Hemminger <stephen@...workplumber.org>
Subject: Re: [PATCH net-next V2] net ipv6: convert fib6_table rwlock to a
 percpu lock

On Fri, 2017-08-04 at 09:38 -0700, Shaohua Li wrote:
> From: Shaohua Li <shli@...com>
> 
> In a syn flooding test, the fib6_table rwlock is a significant
> bottleneck. While converting the rwlock to rcu sounds straighforward,
> but is very challenging if it's possible. A percpu spinlock (lglock has
> been removed from kernel, so I added a simple implementation here) is
> quite trival for this problem since updating the routing table is a rare
> event. In my test, the server receives around 1.5 Mpps in syn flooding
> test without the patch in a dual sockets and 56-CPU system. With the
> patch, the server receives around 3.8Mpps, and perf report doesn't show
> the locking issue.
> 
> Of course the percpu lock isn't as good as rcu, so this isn't intended
> to replace rcu, but this is much better than current readwrite lock.
> Before we have a rcu implementation, this is a good temporary solution.
> Plus, this is a trival change, there is nothing to prevent pursuing a
> rcu implmentation.
> 
> Cc: Wei Wang <weiwan@...gle.com>
> Cc: Eric Dumazet <eric.dumazet@...il.com>
> Cc: Stephen Hemminger <stephen@...workplumber.org>
> Signed-off-by: Shaohua Li <shli@...com>
> ---

Wei has almost done the RCU conversion.

This patch is probably coming too late.