netdev - Re: IPv6 regression introduced by commit 3b6761d18bc11f2af2a6fc494e9026d39593f22c

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Date:   Tue, 10 Mar 2020 09:27:53 -0600
From:   David Ahern <dsahern@...il.com>
To:     Alarig Le Lay <alarig@...rdarmor.fr>
Cc:     netdev@...r.kernel.org, jack@...ilfillan.uk,
        Vincent Bernat <bernat@...ian.org>
Subject: Re: IPv6 regression introduced by commit
 3b6761d18bc11f2af2a6fc494e9026d39593f22c

On 3/10/20 4:35 AM, Alarig Le Lay wrote:
> On dim.  8 mars 20:15:14 2020, David Ahern wrote:
>> If you are using x86 based CPU you can do this:
>>     perf probe ip6_dst_alloc%return ret=%ax
>>
>>     perf record -e probe:* -a -g -- sleep 10
>>     --> run this during the flapping
>>
>>     perf script
> 
> For this probe I see that: https://paste.swordarmor.fr/raw/pt9b

none of the dst allocations are failing.

Are the failing windows always ~30 seconds long?


> 
>> this will show if the flapping is due to dst alloc failures.
>>
>> Other things to try:
>>     perf probe ip6_dst_gc
>>     perf stat -e probe:* -a -I 1000
>>     --> will show calls/sec to running dst gc
> 
> https://paste.swordarmor.fr/raw/uBnm

This is not lining up with dst allocations above. gc function is only
invoked from dst_alloc, and for ipv6 all dst allocations go through
ip6_dst_alloc.

> 
>>     perf probe __ip6_rt_update_pmtu
>>     perf stat -e probe:* -a -I 1000
>>     --> will show calls/sec to mtu updating
> 
> This probe always stays at 0 even when the NDP is failing.
>  
>>     perf probe rt6_insert_exception
>>     perf state -e probe:* -a -I 1000
>>     --> shows calls/sec to inserting exceptions
> 
> Same as the last one.

so no exception handling.

How many ipv6 sockets are open? (ss -6tpn)

How many ipv6 neighbor entries exist? (ip -6 neigh sh)