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

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Date:   Fri, 4 Aug 2017 11:11:40 -0600
From:   David Ahern <dsahern@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>, 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 8/4/17 11:07 AM, Eric Dumazet wrote:
> 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.


+1

I'd rather see the RCU conversion than a move to per-cpu locks.