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:   Thu, 14 Nov 2019 08:39:58 -0700
From:   David Ahern <dsahern@...il.com>
To:     hujunwei <hujunwei4@...wei.com>,
        Eric Dumazet <eric.dumazet@...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 11/14/19 6:04 AM, hujunwei wrote:
> Hi David,
> 
> On 2019/11/12 9:35, David Ahern wrote:
>> On 11/11/19 6:26 PM, hujunwei wrote:
>>>
>>>
>>> Hi Eric,
>>> I applied the patch and find packetes still drop with default value of gc_thresh.
>>> I will submit a patch later.
>>>
>>> Regards Junwei
>>>
>>
>> perhaps it is time to update IPv6's gc_thresh to match IPv4's - meaning
>> it stays but gets set to -1 and is not used. Is there a reason to keep a
>> limit these days?
>>
> I think it is unnecessary to keep this limit, because the default gc_thresh will result in ipv6 packet loss in low ipv6 traffic.
> There are two solutions:
> 1) Why not check the percpu route first in ip6_pol_route_lookup() when rt6_find_cached_rt() retrun NULL, just like ip6_pol_route(). Can anyone help to answer this?

AIUI it's different for no specific reason - just a different lookup
written for different use cases.

ip6_route_lookup for example (which is what netfilter code is using)
does not even need an rt6_info, it just wants to know the lookup is good
and check the egress device. Meaning, all it really needs is the
fib6_info from the lookup under rcu. That (or helper to validate the
lookup and device) is the right long term solution, but a much bigger
change that I have time for right now.


> 2) like you said, set gc_thresh to -1.
> 
> Regards Junwei
>