Another interesting thing, enabling usbmon will increase performance a lot.
root@tom-panda:~# dd if=/dev/sda iflag=direct of=/dev/null bs=128K count=32 32+0 records in 32+0 records out 4194304 bytes (4.2 MB) copied, 3.4598 s, 1.2 MB/s root@tom-panda:~# cat /sys/kernel/debug/usb/usbmon/1u > /tmp/usbmon-1u& [1] 1485 root@tom-panda:~# dd if=/dev/sda iflag=direct of=/dev/null bs=128K count=32 32+0 records in 32+0 records out 4194304 bytes (4.2 MB) copied, 0.795455 s, 5.3 MB/s root@tom-panda:~# dd if=/dev/sda iflag=direct of=/dev/null bs=128K count=32 32+0 records in 32+0 records out 4194304 bytes (4.2 MB) copied, 0.278628 s, 15.1 MB/s root@tom-panda:~# killall -9 cat [1]+ Killed cat /sys/kernel/debug/usb/usbmon/1u > /tmp/usbmon-1u root@tom-panda:~# dd if=/dev/sda iflag=direct of=/dev/null bs=128K count=32 32+0 records in 32+0 records out 4194304 bytes (4.2 MB) copied, 5.0556 s, 830 kB/s root@tom-panda:~# dd if=/dev/sda iflag=direct of=/dev/null bs=128K count=32 32+0 records in 32+0 records out 4194304 bytes (4.2 MB) copied, 3.2009 s, 1.3 MB/s
Another interesting thing, enabling usbmon will increase performance a lot.
root@tom-panda:~# dd if=/dev/sda iflag=direct of=/dev/null bs=128K count=32 debug/usb/ usbmon/ 1u > /tmp/usbmon-1u& debug/usb/ usbmon/ 1u > /tmp/usbmon-1u
32+0 records in
32+0 records out
4194304 bytes (4.2 MB) copied, 3.4598 s, 1.2 MB/s
root@tom-panda:~# cat /sys/kernel/
[1] 1485
root@tom-panda:~# dd if=/dev/sda iflag=direct of=/dev/null bs=128K count=32
32+0 records in
32+0 records out
4194304 bytes (4.2 MB) copied, 0.795455 s, 5.3 MB/s
root@tom-panda:~# dd if=/dev/sda iflag=direct of=/dev/null bs=128K count=32
32+0 records in
32+0 records out
4194304 bytes (4.2 MB) copied, 0.278628 s, 15.1 MB/s
root@tom-panda:~# killall -9 cat
[1]+ Killed cat /sys/kernel/
root@tom-panda:~# dd if=/dev/sda iflag=direct of=/dev/null bs=128K count=32
32+0 records in
32+0 records out
4194304 bytes (4.2 MB) copied, 5.0556 s, 830 kB/s
root@tom-panda:~# dd if=/dev/sda iflag=direct of=/dev/null bs=128K count=32
32+0 records in
32+0 records out
4194304 bytes (4.2 MB) copied, 3.2009 s, 1.3 MB/s