netdev - Re: [PATCH net-next] tcp: add SNMP counter for the number of packets pruned from ofo queue

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Date:   Thu, 26 Jul 2018 09:42:50 +0800
From:   Yafang Shao <laoar.shao@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     David Miller <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next] tcp: add SNMP counter for the number of packets
 pruned from ofo queue

On Wed, Jul 25, 2018 at 9:59 PM, Yafang Shao <laoar.shao@...il.com> wrote:
> On Wed, Jul 25, 2018 at 9:55 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>>
>>
>> On 07/25/2018 06:40 AM, Yafang Shao wrote:
>>
>>>
>>> Because we want to know why packets were dropped.
>>> If that could be show in netstat, we could easily find that it is
>>> dropped due to ofo prune.
>>
>>
>> We have a counter already for these events : LINUX_MIB_OFOPRUNED
>>
>> You want to add another counter tracking number of _skbs_,
>> which has no precise value for user,
>> given each skb can contain a variable number of _packets_.
>>
>
> Got it.
>
> But with LINUX_MIB_OFOPRUNED, we only know  tcp_prune_ofo_queue is
> called, but have no idea how many skbs are dropped.
>


Hi Eric,

LINUX_MIB_TCPOFOQUEUE, LINUX_MIB_TCPOFODROP and LINUX_MIB_TCPOFOMERGE
are all for the number of SKBs, but only  LINUX_MIB_OFOPRUNED is for
the event, that could lead misunderstading.
So I think introducing a counter for the number of SKB pruned could be
better, that could help us to track the whole behavior of ofo queue.
That is why I submit this patch.


Thanks
Yafang