netdev - Re: Bypass at packet-page level (Was: Optimizing instruction-cache, more packets at each stage)

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Message-ID: <1453999417.7627.45.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Thu, 28 Jan 2016 08:43:37 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Tom Herbert <tom@...bertland.com>
Cc:	Jesper Dangaard Brouer <brouer@...hat.com>,
	John Fastabend <john.fastabend@...il.com>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	David Miller <davem@...emloft.net>,
	Or Gerlitz <gerlitz.or@...il.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	Alexander Duyck <alexander.duyck@...il.com>,
	Alexei Starovoitov <alexei.starovoitov@...il.com>,
	Daniel Borkmann <borkmann@...earbox.net>,
	Marek Majkowski <marek@...udflare.com>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	Florian Westphal <fw@...len.de>,
	Paolo Abeni <pabeni@...hat.com>,
	John Fastabend <john.r.fastabend@...el.com>,
	Amir Vadai <amirva@...il.com>,
	Daniel Borkmann <daniel@...earbox.net>,
	Vladislav Yasevich <vyasevich@...il.com>
Subject: Re: Bypass at packet-page level (Was: Optimizing instruction-cache,
 more packets at each stage)

On Thu, 2016-01-28 at 08:37 -0800, Tom Herbert wrote:

> skbs are enqueued on a CPU queue one at at time through
> enqueue_to_backlog. It would be nice to do that as a batch of skbs.

Adding yet another layer and cache misses.

This might be a win for stress situations, not for nominal traffic,
when very few packets are delivered per NAPI poll.

For stress situations, we do not rely on RPS/RFS at all, but prefer RSS
and appropriate number of RX queues, to have true silos.

For the router case, where Jesper wants 15 Mpps on a single core,
RPS/RFS is not used.