netdev - Re: [RFC PATCH 08/13] net: sched: support skb_bad

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Date:   Tue, 23 Aug 2016 13:11:21 -0700
From:   John Fastabend <john.fastabend@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     xiyou.wangcong@...il.com, jhs@...atatu.com,
        alexei.starovoitov@...il.com, brouer@...hat.com,
        john.r.fastabend@...el.com, netdev@...r.kernel.org,
        davem@...emloft.net
Subject: Re: [RFC PATCH 08/13] net: sched: support skb_bad_tx with lockless
 qdisc

On 16-08-17 04:00 PM, John Fastabend wrote:
> On 16-08-17 03:58 PM, Eric Dumazet wrote:
>> On Wed, 2016-08-17 at 12:36 -0700, John Fastabend wrote:
>>> Similar to how gso is handled skb_bad_tx needs to be per cpu to handle
>>> lockless qdisc with multiple writer/producers.
>> \
>>> @@ -1021,6 +1026,7 @@ err_out4:
>>>  	free_percpu(sch->cpu_bstats);
>>>  	free_percpu(sch->cpu_qstats);
>>>  	free_percpu(sch->gso_cpu_skb);
>>> +	free_percpu(sch->skb_bad_txq_cpu);
>>
>>
>> This might be the time to group all these per cpu allocations to a
>> single one, to help data locality and decrease overhead of having XX
>> pointers.
>>
>>
>>
> 
> Sounds like a good idea to me. I'll go ahead and add a patch to the
> front to consolidate the stats and then add these there.
> 

Actually this turned out to be not so trivial. To do it reasonably
requires changes in how gnet stats work and such. I'm going to propose
pushing this into a series after the initial lockless set otherwise the
patch set is going to start pushing 20+ patches.

Also a follow on series to make all the qdiscs support per cpu stats
would be nice and allows us to remove a lot of the annoying if/else
cases around stats. Its a bit tedious to go and change all the qdiscs
but mostly mechanical.

.John