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

[Alexander Lobakin <bloodyreaper@yandex.ru>]

06.04.2020, 18:21, "Alexander Lobakin" <bloodyreaper@yandex.ru>:
> 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.

OK, so here we go.

My device is 1.2 GHz 4-core MIPS32 R2. Ethernet controller representing
the CPU port is capable of S/G, fraglists S/G, TSO4/6 and GSO UDP L4.
Tests are performed through simple IPoE VLAN NAT forwarding setup
(port0 <-> port1.218) with iperf3 in TCP mode.
net.core.gro_normal_batch is always set to 16 as that value seems to be
the most effective for that particular hardware and drivers.

Packet counters on eth0 are the real numbers of ongoing frames. Counters
on portX are pure-software and are updated inside networking stack.

---------------------------------------------------------------------

netif_receive_skb() in Eth driver, no patch:

[ ID] Interval           Transfer     Bitrate         Retr
[  5]   0.00-120.01 sec  9.00 GBytes   644 Mbits/sec  413  sender
[  5]   0.00-120.00 sec  8.99 GBytes   644 Mbits/sec       receiver

eth0
RX packets:7097731 errors:0 dropped:0 overruns:0 frame:0
TX packets:7097702 errors:0 dropped:0 overruns:0 carrier:0

port0
RX packets:426050 errors:0 dropped:0 overruns:0 frame:0
TX packets:6671829 errors:0 dropped:0 overruns:0 carrier:0

port1
RX packets:6671681 errors:0 dropped:0 overruns:0 carrier:0
TX packets:425862 errors:0 dropped:0 overruns:0 carrier:0

port1.218
RX packets:6671677 errors:0 dropped:0 overruns:0 frame:0
TX packets:425851 errors:0 dropped:0 overruns:0 carrier:0

---------------------------------------------------------------------

netif_receive_skb_list() in Eth driver, no patch:

[ ID] Interval           Transfer     Bitrate         Retr
[  5]   0.00-120.01 sec  9.48 GBytes   679 Mbits/sec  129  sender
[  5]   0.00-120.00 sec  9.48 GBytes   679 Mbits/sec       receiver

eth0
RX packets:7448098 errors:0 dropped:0 overruns:0 frame:0
TX packets:7448073 errors:0 dropped:0 overruns:0 carrier:0

port0
RX packets:416115 errors:0 dropped:0 overruns:0 frame:0
TX packets:7032121 errors:0 dropped:0 overruns:0 carrier:0

port1
RX packets:7031983 errors:0 dropped:0 overruns:0 frame:0
TX packets:415941 errors:0 dropped:0 overruns:0 carrier:0

port1.218
RX packets:7031978 errors:0 dropped:0 overruns:0 frame:0
TX packets:415930 errors:0 dropped:0 overruns:0 carrier:0

---------------------------------------------------------------------

napi_gro_receive() in Eth driver, no patch:

[ ID] Interval           Transfer     Bitrate         Retr
[  5]   0.00-120.01 sec  10.0 GBytes   718 Mbits/sec  107  sender
[  5]   0.00-120.00 sec  10.0 GBytes   718 Mbits/sec       receiver

eth0
RX packets:7868281 errors:0 dropped:0 overruns:0 frame:0
TX packets:7868267 errors:0 dropped:0 overruns:0 carrier:0

port0
RX packets:429082 errors:0 dropped:0 overruns:0 frame:0
TX packets:7439343 errors:0 dropped:0 overruns:0 carrier:0

port1
RX packets:7439199 errors:0 dropped:0 overruns:0 frame:0
TX packets:428913 errors:0 dropped:0 overruns:0 carrier:0

port1.218
RX packets:7439195 errors:0 dropped:0 overruns:0 frame:0
TX packets:428902 errors:0 dropped:0 overruns:0 carrier:0

=====================================================================

netif_receive_skb() in Eth driver + patch:

[ ID] Interval           Transfer     Bitrate         Retr
[  5]   0.00-120.01 sec  12.2 GBytes   870 Mbits/sec  2267 sender
[  5]   0.00-120.00 sec  12.2 GBytes   870 Mbits/sec       receiver

eth0
RX packets:9474792 errors:0 dropped:0 overruns:0 frame:0
TX packets:9474777 errors:0 dropped:0 overruns:0 carrier:0

port0
RX packets:455200 errors:0 dropped:0 overruns:0 frame:0
TX packets:353288 errors:0 dropped:0 overruns:0 carrier:0

port1
RX packets:9019592 errors:0 dropped:0 overruns:0 frame:0
TX packets:455035 errors:0 dropped:0 overruns:0 carrier:0

port1.218
RX packets:353144 errors:0 dropped:0 overruns:0 frame:0
TX packets:455024 errors:0 dropped:0 overruns:0 carrier:0

---------------------------------------------------------------------

netif_receive_skb_list() in Eth driver + patch:

[ ID] Interval           Transfer     Bitrate         Retr
[  5]   0.00-120.01 sec  11.6 GBytes   827 Mbits/sec  2224 sender
[  5]   0.00-120.00 sec  11.5 GBytes   827 Mbits/sec       receiver

eth0
RX packets:8981651 errors:0 dropped:0 overruns:0 frame:0
TX packets:898187 errors:0 dropped:0 overruns:0 carrier:0

port0
RX packets:436159 errors:0 dropped:0 overruns:0 frame:0
TX packets:335665 errors:0 dropped:0 overruns:0 carrier:0

port1
RX packets:8545492 errors:0 dropped:0 overruns:0 frame:0
TX packets:436071 errors:0 dropped:0 overruns:0 carrier:0

port1.218
RX packets:335593 errors:0 dropped:0 overruns:0 frame:0
TX packets:436065 errors:0 dropped:0 overruns:0 carrier:0

-----------------------------------------------------------

napi_gro_receive() in Eth driver + patch:

[ ID] Interval           Transfer     Bitrate         Retr
[  5]   0.00-120.01 sec  11.8 GBytes   855 Mbits/sec  122  sender
[  5]   0.00-120.00 sec  11.8 GBytes   855 Mbits/sec       receiver

eth0
RX packets:9292214 errors:0 dropped:0 overruns:0 frame:0
TX packets:9292190 errors:0 dropped:0 overruns:0 carrier:0

port0
RX packets:438516 errors:0 dropped:0 overruns:0 frame:0
TX packets:347236 errors:0 dropped:0 overruns:0 carrier:0

port1
RX packets:8853698 errors:0 dropped:0 overruns:0 frame:0
TX packets:438331 errors:0 dropped:0 overruns:0 carrier:0

port1.218
RX packets:347082 errors:0 dropped:0 overruns:0 frame:0
TX packets:438320 errors:0 dropped:0 overruns:0 carrier:0

-----------------------------------------------------------

The main goal is achieved: we have about 100-200 Mbps of performance
boost while in-stack skbs are greatly reduced from ~8-9 millions to
~350000 (compare port0 TX and port1 RX without patch and with it).

The main bottleneck in gro_cells setup is that GRO layer starts to
work only after skb are being processed by DSA stack, so they are
going frame-by-frame until that moment (RX counter on port1).

If one day we change the way of handling incoming packets (not
through fake packet_type), we could avoid that by unblocking GRO
processing in between Eth driver and DSA core.
With my custom packet_offload for ETH_P_XDSA that works only for
my CPU tag format I have about ~910-920 Mbps on the same platform.
This way doesn't fit mainline code of course, so I'm working on
alternative Rx paths for DSA, e.g. through net_device::rx_handler()
etc.

Until then, gro_cells really improve things a lot while the actual
patch is tiny.

>>       Andrew

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