netdev - Re: ping6 packets high probability loss occurs by the default firewalld rule(rpfilter invert) with low traffic generated by iperf

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Date:   Sun, 3 Nov 2019 10:53:50 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     hujunwei <hujunwei4@...wei.com>, dsahern@...il.com,
        davem@...emloft.net, kafai@...com, weiwan@...gle.com
Cc:     netdev@...r.kernel.org, wangxiaogang3@...wei.com,
        xuhanbing@...wei.com
Subject: Re: ping6 packets high probability loss occurs by the default
 firewalld rule(rpfilter invert) with low traffic generated by iperf



On 11/3/19 1:32 AM, hujunwei wrote:
> 
> Afer debugging, I find that packet drop because system can't alloc ipv6 dst. when dst->pcpuc_entries exceed gc_thresh in dst_alloc() which called by rpfilter_lookup_reverse6().
> When I increase gc_thresh, packets loss decreased, but I think it is unreasonable to lose packets by default firewalld rule with low traffic.
> 


By how much have you increased gc_thresh ?

I wonder if you are not hit by RCU being unable to drain its queue fast enough.

Could you try backporting :

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=cfcdef5e30469f3f2d6786ad35fc3fdef2a3833f

But the default gc_thresh of 1024 might be too small for this patch
to make any difference, since (1024 >> 7) is 8