Dear Piergiorgio,

In message [ref] you wrote:

raid6check is CPU bounded, no vector optimization
and no multithread.

Nevertheless, if you see no CPU load (single core
load), then something else is not OK, but I've no
idea what it could be.

Please check if one core is up 100%, if this is
the case, then there is the limit.
If not, sorry, I cannot help.

No, there is virtually no CPU load at all:

top - 08:32:36 up 8 days, 16:34,  3 users,  load average: 1.00, 1.01, 1.00
Tasks: 243 total,   1 running, 242 sleeping,   0 stopped,   0 zombie
%Cpu0  :  0.0 us,  0.0 sy,  0.0 ni, 98.7 id,  0.0 wa,  1.3 hi,  0.0 si,  0.0 st
%Cpu1  :  0.0 us,  0.0 sy,  0.0 ni,100.0 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
%Cpu2  :  0.0 us,  0.0 sy,  0.0 ni,100.0 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
%Cpu3  :  0.3 us,  1.3 sy,  0.0 ni, 97.7 id,  0.0 wa,  0.3 hi,  0.3 si,  0.0 st
%Cpu4  :  0.0 us,  0.0 sy,  0.0 ni,100.0 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
%Cpu5  :  1.7 us,  3.7 sy,  0.0 ni, 90.4 id,  3.0 wa,  0.7 hi,  0.7 si,  0.0 st
%Cpu6  :  0.0 us,  0.0 sy,  0.0 ni,100.0 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
%Cpu7  :  0.0 us,  0.0 sy,  0.0 ni,100.0 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
MiB Mem :  24034.6 total,  10921.2 free,   1882.4 used,  11230.9 buff/cache
MiB Swap:   7828.5 total,   7828.5 free,      0.0 used.  21757.0 avail Mem

What I find interesting is thet all disks are more or less
constantly at around 400 kB/s (390...400, never more).

Best regards,

Wolfgang Denk

-- 
DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd@denx.de
That's their goal, remember, a goal that's really contrary to that of
the programmer or administrator. We just want to get our  jobs  done.
$Bill  just  wants  to  become  $$Bill. These aren't even marginallly
congruent.
         -- Tom Christiansen in [off-list ref]