netdev - Re: [PATCH v2 net-next 1/1] net: netem: use a list in addition to rbtree

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Message-Id: <20181205.201854.1999807195414205821.davem@davemloft.net>
Date:   Wed, 05 Dec 2018 20:18:54 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     posk@...gle.com
Cc:     netdev@...r.kernel.org, posk.devel@...il.com, edumazet@...gle.com,
        stephen@...workplumber.org
Subject: Re: [PATCH v2 net-next 1/1] net: netem: use a list in addition to
 rbtree

From: Peter Oskolkov <posk@...gle.com>
Date: Tue,  4 Dec 2018 11:55:56 -0800

> When testing high-bandwidth TCP streams with large windows,
> high latency, and low jitter, netem consumes a lot of CPU cycles
> doing rbtree rebalancing.
> 
> This patch uses a linear list/queue in addition to the rbtree:
> if an incoming packet is past the tail of the linear queue, it is
> added there, otherwise it is inserted into the rbtree.
> 
> Without this patch, perf shows netem_enqueue, netem_dequeue,
> and rb_* functions among the top offenders. With this patch,
> only netem_enqueue is noticeable if jitter is low/absent.
> 
> Suggested-by: Eric Dumazet <edumazet@...gle.com>
> Signed-off-by: Peter Oskolkov <posk@...gle.com>

Applied, thanks.