linux-kernel - Re: [PATCH] IPIP tunnel performance improvement

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Date:	Fri, 26 Feb 2016 22:29:51 -0800
From:	Cong Wang <xiyou.wangcong@...il.com>
To:	zhao ya <marywangran0627@...il.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH] IPIP tunnel performance improvement

On Fri, Feb 26, 2016 at 8:40 PM, zhao ya <marywangran0627@...il.com> wrote:
> From: Zhao Ya <marywangran0627@...il.com>
> 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 <davem@...emloft.net>
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 <eric.dumazet@...il.com>
    Signed-off-by: David S. Miller <davem@...emloft.net>

which would bring the neigh entries counting problem back...

Did you try to tune the neigh gc parameters for your case?

Thanks.