Sami Kantoluoto sami.kantoluoto@embedtronics.fi wrote;

> When dd hangs (reading normal device), it's waiting "biowait".

"lost interrupt" which notify xfer has done.  Upper half device driver
waits for notification to proceed and is waiting forever.

> Interestingly, reading raw device gives me 3.3 MB but reading
> normal device gives 2.3 MB (and CPU is 7.7 % idle)..

Raw device access can be faster than block I/O buffer access since
HW may allow to have much larger xfer chunk size than FS block
size, 8KB or 16KB typical.

Toru Nishimura/ALKYL Technology