riscv: optimized memcpy
Write a C version of memcpy() which uses the biggest data size allowed,
without generating unaligned accesses.
The procedure is made of three steps:
First copy data one byte at time until the destination buffer is aligned
to a long boundary.
Then copy the data one long at time shifting the current and the next u8
to compose a long at every cycle.
Finally, copy the remainder one byte at time.
On a BeagleV, the TCP RX throughput increased by 45%:
before:
$ iperf3 -c beaglev
Connecting to host beaglev, port 5201
[ 5] local 192.168.85.6 port 44840 connected to 192.168.85.48 port 5201
[ ID] Interval Transfer Bitrate Retr Cwnd
[ 5] 0.00-1.00 sec 76.4 MBytes 641 Mbits/sec 27 624 KBytes
[ 5] 1.00-2.00 sec 72.5 MBytes 608 Mbits/sec 0 708 KBytes
[ 5] 2.00-3.00 sec 73.8 MBytes 619 Mbits/sec 10 451 KBytes
[ 5] 3.00-4.00 sec 72.5 MBytes 608 Mbits/sec 0 564 KBytes
[ 5] 4.00-5.00 sec 73.8 MBytes 619 Mbits/sec 0 658 KBytes
[ 5] 5.00-6.00 sec 73.8 MBytes 619 Mbits/sec 14 522 KBytes
[ 5] 6.00-7.00 sec 73.8 MBytes 619 Mbits/sec 0 621 KBytes
[ 5] 7.00-8.00 sec 72.5 MBytes 608 Mbits/sec 0 706 KBytes
[ 5] 8.00-9.00 sec 73.8 MBytes 619 Mbits/sec 20 580 KBytes
[ 5] 9.00-10.00 sec 73.8 MBytes 619 Mbits/sec 0 672 KBytes
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bitrate Retr
[ 5] 0.00-10.00 sec 736 MBytes 618 Mbits/sec 71 sender
[ 5] 0.00-10.01 sec 733 MBytes 615 Mbits/sec receiver
after:
$ iperf3 -c beaglev
Connecting to host beaglev, port 5201
[ 5] local 192.168.85.6 port 44864 connected to 192.168.85.48 port 5201
[ ID] Interval Transfer Bitrate Retr Cwnd
[ 5] 0.00-1.00 sec 109 MBytes 912 Mbits/sec 48 559 KBytes
[ 5] 1.00-2.00 sec 108 MBytes 902 Mbits/sec 0 690 KBytes
[ 5] 2.00-3.00 sec 106 MBytes 891 Mbits/sec 36 396 KBytes
[ 5] 3.00-4.00 sec 108 MBytes 902 Mbits/sec 0 567 KBytes
[ 5] 4.00-5.00 sec 106 MBytes 891 Mbits/sec 0 699 KBytes
[ 5] 5.00-6.00 sec 106 MBytes 891 Mbits/sec 32 414 KBytes
[ 5] 6.00-7.00 sec 106 MBytes 891 Mbits/sec 0 583 KBytes
[ 5] 7.00-8.00 sec 106 MBytes 891 Mbits/sec 0 708 KBytes
[ 5] 8.00-9.00 sec 106 MBytes 891 Mbits/sec 28 433 KBytes
[ 5] 9.00-10.00 sec 108 MBytes 902 Mbits/sec 0 591 KBytes
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bitrate Retr
[ 5] 0.00-10.00 sec 1.04 GBytes 897 Mbits/sec 144 sender
[ 5] 0.00-10.01 sec 1.04 GBytes 894 Mbits/sec receiver
And the decreased CPU time of the memcpy() is observable with perf top.
This is the `perf top -Ue task-clock` output when doing the test:
before:
Overhead Shared O Symbol
42.22% [kernel] [k] memcpy
35.00% [kernel] [k] __asm_copy_to_user
3.50% [kernel] [k] sifive_l2_flush64_range
2.30% [kernel] [k] stmmac_napi_poll_rx
1.11% [kernel] [k] memset
after:
Overhead Shared O Symbol
45.69% [kernel] [k] __asm_copy_to_user
29.06% [kernel] [k] memcpy
4.09% [kernel] [k] sifive_l2_flush64_range
2.77% [kernel] [k] stmmac_napi_poll_rx
1.24% [kernel] [k] memset
Signed-off-by: Matteo Croce <mcroce@microsoft.com>
Signed-off-by: Emil Renner Berthing <kernel@esmil.dk>