netdev - Re: High Cpu load when run smartdns : __ipv6_dev_get

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Date: Sun, 27 Aug 2023 20:42:03 -0600
From: David Ahern <dsahern@...nel.org>
To: Martin Zaharinov <micron10@...il.com>
Cc: netdev <netdev@...r.kernel.org>, Eric Dumazet <edumazet@...gle.com>,
 pymumu@...il.com
Subject: Re: High Cpu load when run smartdns : __ipv6_dev_get_saddr

On 8/27/23 1:17 PM, Martin Zaharinov wrote:
> Hi David,
> 
> 
> 
>> On 27 Aug 2023, at 19:51, David Ahern <dsahern@...nel.org> wrote:
>>
>> On 8/27/23 7:20 AM, Martin Zaharinov wrote:
>>> Hi Eric 
>>>
>>>
>>> i need you help to find is this bug or no.
>>>
>>> I talk with smartdns team and try to research in his code but for the moment not found ..
>>>
>>> test system have 5k ppp users on pppoe device
>>>
>>> after run smartdns  
>>>
>>> service got to 100% load 
>>>
>>> in normal case when run other 2 type of dns server (isc bind or knot ) all is fine .
>>>
>>> but when run smartdns  see perf : 
>>>
>>>
>>> PerfTop:    4223 irqs/sec  kernel:96.9%  exact: 100.0% lost: 0/0 drop: 0/0 [4000Hz cycles],  (target_pid: 1208268)
>>> ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
>>>
>>>    28.48%  [kernel]        [k] __ipv6_dev_get_saddr
>>>    12.31%  [kernel]        [k] l3mdev_master_ifindex_rcu
>>>     6.63%  [pppoe]         [k] pppoe_rcv
>>>     3.82%  [kernel]        [k] ipv6_dev_get_saddr
>>>     2.07%  [kernel]        [k] __dev_queue_xmit
>>
>> Can you post stack traces for the top 5 symbols?
> 
> If write how i will get.

While running traffic load:
    perf record -a -g -- sleep 5
    perf report --stdio

> 
>>
>> What is the packet rate when the above is taken?
> 
> its normal rate of dns query… with both other dns server all is fine 

That means nothing to me. You will need to post packet rates.

> 
>>
>> 4,223 irqs/sec is not much of a load; can you add some details on the
>> hardware and networking setup (e.g., l3mdev reference suggests you are
>> using VRF)?
> No system is very simple:
> 
> eth0 (Internet) Router (smartDNS + pppoe server ) - eth1 ( User side with pppoe server ) here have 5000 ppp interface .
> 
> with both other service i dont see all work fine.

ip link sh type vrf
--> that does not show any devices? It should because the majority of
work done in l3mdev_master_ifindex_rcu is for vrf port devices. ie., it
should not appear in the perf-top data you posted unless vrf devices are
in play.