netdev - Re: [PATCH net-next 03/13] net: sched: extend Qdisc with rcu

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Date:   Thu, 6 Sep 2018 02:21:53 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Kirill Tkhai <ktkhai@...tuozzo.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Vlad Buslov <vladbu@...lanox.com>, netdev@...r.kernel.org
Cc:     jhs@...atatu.com, xiyou.wangcong@...il.com, jiri@...nulli.us,
        davem@...emloft.net, stephen@...workplumber.org,
        paulmck@...ux.vnet.ibm.com, nicolas.dichtel@...nd.com,
        leon@...nel.org, gregkh@...uxfoundation.org, mark.rutland@....com,
        fw@...len.de, dsahern@...il.com, lucien.xin@...il.com,
        jakub.kicinski@...ronome.com, christian.brauner@...ntu.com,
        jbenc@...hat.com
Subject: Re: [PATCH net-next 03/13] net: sched: extend Qdisc with rcu



On 09/06/2018 01:39 AM, Kirill Tkhai wrote:
> On 06.09.2018 11:30, Eric Dumazet wrote:
>>
>>
>> On 09/06/2018 12:58 AM, Vlad Buslov wrote:
>>
>> ...
>>
>>> diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
>>> index 18e22a5a6550..239c73f29471 100644
>>> --- a/include/net/sch_generic.h
>>> +++ b/include/net/sch_generic.h
>>> @@ -90,6 +90,7 @@ struct Qdisc {
>>>  	struct gnet_stats_queue	__percpu *cpu_qstats;
>>>  	int			padded;
>>>  	refcount_t		refcnt;
>>> +	struct rcu_head		rcu;
>>>  
>>>  	/*
>>>  	 * For performance sake on SMP, we put highly modified fields at the end
>>
>> Probably better to move this at the end of struct Qdisc,
>> not risking unexpected performance regressions in fast path.
> 
> Do you mean regressions on UP? On SMP it looks like this field
> fits in the unused gap created by:
> 
> 	struct sk_buff_head     gso_skb ____cacheline_aligned_in_smp;
> 
> Kirill

Oh right, we might have holes there, and in the last cache line, so it does not
matter for now.