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

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Date:   Fri, 4 Aug 2017 10:20:05 -0700
From:   Wei Wang <weiwan@...gle.com>
To:     David Ahern <dsahern@...il.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Shaohua Li <shli@...nel.org>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        "David S . Miller" <davem@...emloft.net>, Kernel-team@...com,
        Shaohua Li <shli@...com>,
        Stephen Hemminger <stephen@...workplumber.org>
Subject: Re: [PATCH net-next V2] net ipv6: convert fib6_table rwlock to a
 percpu lock

On Fri, Aug 4, 2017 at 10:11 AM, David Ahern <dsahern@...il.com> wrote:
> 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.

I am actively working on the RCU conversion.
The main coding part is mostly done and I am working on testing it.
Some more time is needed to catch the rest of the missing pieces and
get the patches ready.

Thanks.
Wei