netdev - Re: [RFC PATCH 01/13] net: sched: allow qdiscs to handle locking

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Date:	Wed, 17 Aug 2016 15:33:00 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	John Fastabend <john.fastabend@...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 01/13] net: sched: allow qdiscs to handle locking

On Wed, 2016-08-17 at 12:33 -0700, John Fastabend wrote:
> This patch adds a flag for queueing disciplines to indicate the stack
> does not need to use the qdisc lock to protect operations. This can
> be used to build lockless scheduling algorithms and improving
> performance.
> 
> The flag is checked in the tx path and the qdisc lock is only taken
> if it is not set. For now use a conditional if statement. Later we
> could be more aggressive if it proves worthwhile and use a static key
> or wrap this in a likely().
> 
> Signed-off-by: John Fastabend <john.r.fastabend@...el.com>
> ---
>  include/net/pkt_sched.h   |    4 +++-
>  include/net/sch_generic.h |    1 +
>  net/core/dev.c            |   32 ++++++++++++++++++++++++++++----
>  net/sched/sch_generic.c   |   26 ++++++++++++++++----------
>  4 files changed, 48 insertions(+), 15 deletions(-)
> 
> diff --git a/include/net/pkt_sched.h b/include/net/pkt_sched.h
> index 7caa99b..69540c6 100644
> --- a/include/net/pkt_sched.h
> +++ b/include/net/pkt_sched.h
> @@ -107,8 +107,10 @@ void __qdisc_run(struct Qdisc *q);
>  
>  static inline void qdisc_run(struct Qdisc *q)
>  {
> -	if (qdisc_run_begin(q))
> +	if (qdisc_run_begin(q)) {
>  		__qdisc_run(q);
> +		qdisc_run_end(q);
> +	}
>  }


Looks like you could have a separate patch, removing qdisc_run_end()
call done in __qdisc_run(q) ?

Then the 'allow qdiscs to handle locking'