Subject: Re: [PATCH] IPIP tunnel performance improvement

From: zhao ya <[email-masked]>
Date: Sat, 27 Feb 2016 15:06:30 +0800

Yes, I did, but have no effect.

I want to ask is, why David's patch not used.

Thanks.

Cong Wang said, at 2/27/2016 2:29 PM:
> On Fri, Feb 26, 2016 at 8:40 PM, zhao ya <[email-masked]> wrote:
>> From: Zhao Ya <[email-masked]>
>> Date: Sat, 27 Feb 2016 10:06:44 +0800
>> Subject: [PATCH] IPIP tunnel performance improvement
>>
>> bypass the logic of each packet's own neighbour creation when using
>> pointopint or loopback device.
>>
>> Recently, in our tests, met a performance problem.
>> In a large number of packets with different target IP address through
>> ipip tunnel, PPS will decrease sharply.
>>
>> The output of perf top are as follows, __write_lock_failed is of the first:
>>   - 5.89% [kernel]              [k] __write_lock_failed
>>    -__write_lock_failed                                         a
>>    -_raw_write_lock_bh                                          a
>>    -__neigh_create                                              a
>>    -ip_finish_output                                            a
>>    -ip_output                                                   a
>>    -ip_local_out                                                a
>>
>> The neighbour subsystem will create a neighbour object for each target
>> when using pointopint device. When massive amounts of packets with diff-
>> erent target IP address to be xmit through a pointopint device, these
>> packets will suffer the bottleneck at write_lock_bh(&tbl->lock) after
>> creating the neighbour object and then inserting it into a hash-table
>> at the same time.
>>
>> This patch correct it. Only one or little amounts of neighbour objects
>> will be created when massive amounts of packets with different target IP
>> address through ipip tunnel.
>>
>> As the result, performance will be improved.
> 
> Well, you just basically revert another bug fix:
> 
> commit 0bb4087cbec0ef74fd416789d6aad67957063057
> Author: David S. Miller <[email-masked]>
> Date:   Fri Jul 20 16:00:53 2012 -0700
> 
>     ipv4: Fix neigh lookup keying over loopback/point-to-point devices.
> 
>     We were using a special key "0" for all loopback and point-to-point
>     device neigh lookups under ipv4, but we wouldn't use that special
>     key for the neigh creation.
> 
>     So basically we'd make a new neigh at each and every lookup :-)
> 
>     This special case to use only one neigh for these device types
>     is of dubious value, so just remove it entirely.
> 
>     Reported-by: Eric Dumazet <[email-masked]>
>     Signed-off-by: David S. Miller <[email-masked]>
> 
> which would bring the neigh entries counting problem back...
> 
> Did you try to tune the neigh gc parameters for your case?
> 
> Thanks.
>