Re: [PATCH net-next] net: dsa: add GRO support via gro_cells

From: Alexander Lobakin <bloodyreaper@yandex.ru>
To: Andrew Lunn <andrew@lunn.ch>
Cc: Woojung Huh <woojung.huh@microchip.com>,
	Florian Fainelli <f.fainelli@gmail.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Hauke Mehrtens <hauke@hauke-m.de>,
	Linus Walleij <linus.walleij@linaro.org>,
	Sean Wang <sean.wang@mediatek.com>,
	Russell King <linux@armlinux.org.uk>,
	Vivien Didelot <vivien.didelot@gmail.com>,
	Microchip Linux Driver Support <unglinuxdriver@microchip.com>,
	Vladimir Oltean <vladimir.oltean@nxp.com>,
	Claudiu Manoil <claudiu.manoil@nxp.com>,
	"linux-mediatek@lists.infradead.org"
	<linux-mediatek@lists.infradead.org>,
	Philipp Zabel <p.zabel@pengutronix.de>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	Matthias Brugger <matthias.bgg@gmail.com>,
	Jakub Kicinski <kuba@kernel.org>,
	Oleksij Rempel <linux@rempel-privat.de>,
	"David S. Miller" <davem@davemloft.net>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>,
	Mao Wenan <maowenan@huawei.com>
Subject: Re: [PATCH net-next] net: dsa: add GRO support via gro_cells
Date: Mon, 06 Apr 2020 18:21:18 +0300	[thread overview]
Message-ID: <20241586185765@iva8-5e86d95f65ab.qloud-c.yandex.net> (raw)
In-Reply-To: <20200406144758.GC301483@lunn.ch>

06.04.2020, 17:48, "Andrew Lunn" <andrew@lunn.ch>:
> On Mon, Apr 06, 2020 at 01:59:10PM +0300, Alexander Lobakin wrote:
>>  gro_cells lib is used by different encapsulating netdevices, such as
>>  geneve, macsec, vxlan etc. to speed up decapsulated traffic processing.
>>  CPU tag is a sort of "encapsulation", and we can use the same mechs to
>>  greatly improve overall DSA performance.
>>  skbs are passed to the GRO layer after removing CPU tags, so we don't
>>  need any new packet offload types as it was firstly proposed by me in
>>  the first GRO-over-DSA variant [1].
>>
>>  The size of struct gro_cells is sizeof(void *), so hot struct
>>  dsa_slave_priv becomes only 4/8 bytes bigger, and all critical fields
>>  remain in one 32-byte cacheline.
>>  The other positive side effect is that drivers for network devices
>>  that can be shipped as CPU ports of DSA-driven switches can now use
>>  napi_gro_frags() to pass skbs to kernel. Packets built that way are
>>  completely non-linear and are likely being dropped without GRO.
>>
>>  This was tested on to-be-mainlined-soon Ethernet driver that uses
>>  napi_gro_frags(), and the overall performance was on par with the
>>  variant from [1], sometimes even better due to minimal overhead.
>>  net.core.gro_normal_batch tuning may help to push it to the limit
>>  on particular setups and platforms.
>>
>>  [1] https://lore.kernel.org/netdev/20191230143028.27313-1-alobakin@dlink.ru/
>
> Hi Alexander

Hi Andrew!

> net-next is closed at the moment. So you should of posted this with an
> RFC prefix.

I saw that it's closed, but didn't knew about "RFC" tags for that period,
sorry.

> The implementation looks nice and simple. But it would be nice to have
> some performance figures.

I'll do, sure. I think I'll collect the stats with various main receiving
functions in Ethernet driver (napi_gro_frags(), napi_gro_receive(),
netif_receive_skb(), netif_receive_skb_list()), and with and without this
patch to make them as complete as possible.

>      Andrew

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