system response issue

[jd1008]

I started a tar command from
one external eSATA drive (ext4), connected to eSATA port,
out to a USB flash drive (with vfat). The USB stick is touted
to support 50MB/s write, 160MB/s read.
The USB port itself is USB 2.0 (480MBits/s).

The desktop (Mate) response goes down the tubes.
I ran top and found that cpu is only 3% usage by firefox.
rest are a few at 1%, and rest showing 0%.

Load average: load average: 5.95, 5.81, 6.05

Wow!!!! Why?

I ran iotop -d 3 and found
  3263 be/4 root        0.00 B/s    0.00 B/s  0.00 % 99.99 % [kworker/u16:3]
    61 be/4 root        0.00 B/s    0.00 B/s  0.00 % 99.99 % [kswapd0]
  3180 be/4 root      335.95 B/s    3.62 M/s  0.00 % 99.99 % tar -C 
/sdc1 -xpvf -
  4071 be/4 root        0.00 B/s    0.00 B/s  0.00 % 27.36 % [kworker/0:2]

Processes that are started but idle:

1 instance of smplayer (idle - nothing being played)
2 instances of TB (for 2 different profiles) - idle - no incoming or 
outgoing emails.
    both check for mail every so many minutes.
1 instance of FF with a total of 6 tabs - all of them idle (no videos, 
no audios on them
and no animations.).

So, it seems that the scheduler is letting the disk io pretty much
commandeer and hijack system response time for the DT.

Is there a configuration tweak to grant more cycles to the DT (mouse, 
KB) interaction
with other GUI based programs?