Re: [PATCH net-next v2 1/5] lan743x: boost performance on cpu archs w/o dma cache snooping

Sergej Bauer
2021-02-12T00:20:31Z

On Thursday, February 11, 2021 7:18:26 PM MSK you wrote:
> From: Sven Van Asbroeck <thesven73@gmail.com>
>
> The buffers in the lan743x driver's receive ring are always 9K,
> even when the largest packet that can be received (the mtu) is
> much smaller. This performs particularly badly on cpu archs
> without dma cache snooping (such as ARM): each received packet
> results in a 9K dma_{map|unmap} operation, which is very expensive
> because cpu caches need to be invalidated.
>
> Careful measurement of the driver rx path on armv7 reveals that
> the cpu spends the majority of its time waiting for cache
> invalidation.
>
> Optimize by keeping the rx ring buffer size as close as possible
> to the mtu. This limits the amount of cache that requires
> invalidation.
>
> This optimization would normally force us to re-allocate all
> ring buffers when the mtu is changed - a disruptive event,
> because it can only happen when the network interface is down.
>
> Remove the need to re-allocate all ring buffers by adding support
> for multi-buffer frames. Now any combination of mtu and ring
> buffer size will work. When the mtu changes from mtu1 to mtu2,
> consumed buffers of size mtu1 are lazily replaced by newly
> allocated buffers of size mtu2.
>
> These optimizations double the rx performance on armv7.
> Third parties report 3x rx speedup on armv8.
>
> Tested with iperf3 on a freescale imx6qp + lan7430, both sides
> set to mtu 1500 bytes, measure rx performance:
>
> Before:
> [ ID] Interval Transfer Bandwidth Retr
> [ 4] 0.00-20.00 sec 550 MBytes 231 Mbits/sec 0
> After:
> [ ID] Interval Transfer Bandwidth Retr
> [ 4] 0.00-20.00 sec 1.33 GBytes 570 Mbits/sec 0
>
> Signed-off-by: Sven Van Asbroeck <thesven73@gmail.com>
> ---

( for the reference to current speed, response to v1 of the patch can be found at
https://lkml.org/lkml/2021/2/5/472 )

Hi Sven
although whole set of tests might be an overly extensive, but after applying patch v2 [1/5]
tests are:
sbauer@metamini ~/devel/kernel-works/net-next.git lan743x_virtual_phy$ ifmtu eth7 500
mtu = 500
sbauer@metamini ~/devel/kernel-works/net-next.git lan743x_virtual_phy$ sudo test_ber -l eth7 -c 1000 -n 1000000 -f500 --no-conf
...
number of sent packets = 1000000
number of received packets = 747411
number of lost packets = 252589
number of out of order packets = 0
number of bit errors = 0
total errors detected = 252589
bit error rate = 0.252589
average speed: 408.0757 Mbit/s

...
number of sent packets = 1000000
number of received packets = 738377
number of lost packets = 261623
number of out of order packets = 0
number of bit errors = 0
total errors detected = 261623
bit error rate = 0.261623
average speed: 413.1470 Mbit/s

...
number of sent packets = 1000000
number of received packets = 738142
number of lost packets = 261858
number of out of order packets = 0
number of bit errors = 0
total errors detected = 261858
bit error rate = 0.261858
average speed: 413.2262 Mbit/s

...
number of sent packets = 1000000
number of received packets = 708973
number of lost packets = 291027
number of out of order packets = 0
number of bit errors = 0
total errors detected = 291027
bit error rate = 0.291027
average speed: 430.6224 Mbit/s

...
number of sent packets = 1000000
number of received packets = 725452
number of lost packets = 274548
number of out of order packets = 0
number of bit errors = 0
total errors detected = 274548
bit error rate = 0.274548
average speed: 420.7341 Mbit/s

sbauer@metamini ~/devel/kernel-works/net-next.git lan743x_virtual_phy$ ifmtu eth7 1500
mtu = 1500
sbauer@metamini ~/devel/kernel-works/net-next.git lan743x_virtual_phy$ sudo test_ber -l eth7 -c 1000 -n 1000000 -f500 --no-conf
...
number of sent packets = 1000000
number of received packets = 714228
number of lost packets = 285772
number of out of order packets = 0
number of bit errors = 0
total errors detected = 285772
bit error rate = 0.285772
average speed: 427.1300 Mbit/s

...
number of sent packets = 1000000
number of received packets = 750055
number of lost packets = 249945
number of out of order packets = 0
number of bit errors = 0
total errors detected = 249945
bit error rate = 0.249945
average speed: 405.0383 Mbit/s

...
number of sent packets = 1000000
number of received packets = 689458
number of lost packets = 310542
number of out of order packets = 0
number of bit errors = 0
total errors detected = 310542
bit error rate = 0.310542
average speed: 442.5301 Mbit/s

number of sent packets = 1000000
number of received packets = 676830
number of lost packets = 323170
number of out of order packets = 0
number of bit errors = 0
total errors detected = 323170
bit error rate = 0.32317
average speed: 450.9439 Mbit/s

number of sent packets = 1000000
number of received packets = 701719
number of lost packets = 298281
number of out of order packets = 0
number of bit errors = 0
total errors detected = 298281
bit error rate = 0.298281
average speed: 434.7563 Mbit/s

sbauer@metamini ~/devel/kernel-works/net-next.git lan743x_virtual_phy$ sudo test_ber -l eth7 -c 1000 -n 1000000 -f1500 --no-conf
...
number of sent packets = 1000000
number of received packets = 1000000
number of lost packets = 0
number of out of order packets = 0
number of bit errors = 0
total errors detected = 0
bit error rate = 0
average speed: 643.5758 Mbit/s

...
number of sent packets = 1000000
number of received packets = 1000000
number of lost packets = 0
number of out of order packets = 0
number of bit errors = 0
total errors detected = 0
bit error rate = 0
average speed: 644.7713 Mbit/s

...
number of sent packets = 1000000
number of received packets = 1000000
number of lost packets = 0
number of out of order packets = 0
number of bit errors = 0
total errors detected = 0
bit error rate = 0
average speed: 645.4407 Mbit/s

...
number of sent packets = 1000000
number of received packets = 1000000
number of lost packets = 0
number of out of order packets = 0
number of bit errors = 0
total errors detected = 0
bit error rate = 0
average speed: 645.6741 Mbit/s

...
number of sent packets = 1000000
number of received packets = 1000000
number of lost packets = 0
number of out of order packets = 0
number of bit errors = 0
total errors detected = 0
bit error rate = 0
average speed: 646.0109 Mbit/s

sbauer@metamini ~/devel/kernel-works/net-next.git lan743x_virtual_phy$ ifmtu eth7 9216
mtu = 9216
bauer@metamini ~/devel/kernel-works/net-next.git lan743x_virtual_phy$ sudo test_ber -l eth7 -c 1000 -n 1000000 -f1500 --no-conf
...
number of sent packets = 1000000
number of received packets = 575141
number of lost packets = 424859
number of out of order packets = 0
number of bit errors = 0
total errors detected = 424859
bit error rate = 0.424859
average speed: 646.7859 Mbit/s

...
number of sent packets = 1000000
number of received packets = 583353
number of lost packets = 416647
number of out of order packets = 0
number of bit errors = 0
total errors detected = 416647
bit error rate = 0.416647
average speed: 637.8472 Mbit/s

...
number of sent packets = 1000000
number of received packets = 577127
number of lost packets = 422873
number of out of order packets = 0
number of bit errors = 0
total errors detected = 422873
bit error rate = 0.422873
average speed: 644.5562 Mbit/s

...
number of sent packets = 1000000
number of received packets = 576916
number of lost packets = 423084
number of out of order packets = 0
number of bit errors = 0
total errors detected = 423084
bit error rate = 0.423084
average speed: 644.8260 Mbit/s

...
number of sent packets = 1000000
number of received packets = 577154
number of lost packets = 422846
number of out of order packets = 0
number of bit errors = 0
total errors detected = 422846
bit error rate = 0.422846
average speed: 644.6815 Mbit/s

sbauer@metamini ~/devel/kernel-works/net-next.git lan743x_virtual_phy$ sudo test_ber -l eth7 -c 1000 -n 1000000 -f9216 --no-conf
...
number of sent packets = 1000000
number of received packets = 1000000
number of lost packets = 0
number of out of order packets = 0
number of bit errors = 0
total errors detected = 0
bit error rate = 0
average speed: 775.2005 Mbit/s

...
number of sent packets = 1000000
number of received packets = 999998
number of lost packets = 2
number of out of order packets = 0
number of bit errors = 0
total errors detected = 2
bit error rate = 2e-06
average speed: 775.0468 Mbit/

...
number of sent packets = 1000000
number of received packets = 999998
number of lost packets = 2
number of out of order packets = 0
number of bit errors = 0
total errors detected = 2
bit error rate = 2e-06
average speed: 775.2150 Mbit/s

...
number of sent packets = 1000000
number of received packets = 999997
number of lost packets = 3
number of out of order packets = 0
number of bit errors = 0
total errors detected = 3
bit error rate = 3e-06
average speed: 775.2666 Mbit/s

...
number of sent packets = 1000000
number of received packets = 999999
number of lost packets = 1
number of out of order packets = 0
number of bit errors = 0
total errors detected = 1
bit error rate = 1e-06
average speed: 775.2182 Mbit/s