Pádraig Brady wrote:
The CPU percentage of "dd" process sometimes is 30% to 50%,
which is higher than we expect (<= 20%), and there is no other big
program running at the same time.
If the disc in SATA ODD is CD-R instead of DVD-R, the percentage is
much smaller(<=20).
That just means that dd is waiting on the CD-R more than
on the DVD-R as the DVD-R is probably faster.
iowait != busy. It's using cpu time to actively copy data around in ram
or to/from IO ports if not using DMA, not waiting on the hardware.
So my questions are:
(1) Is there an official normal range(or criteria) to the "dd" CPU
percentage?
(2) Can we say that it's abnormal if it is higher than 30% or even 50%?
(3) And what kinds of factors lead to the high CPU percentage of "dd"
and
how to decrease it?
1) No, it entirely depends on your hardware and kernel
2) I certainly don't like to see it even as high as 20% on typical
desktop PC type hardware. I prefer to see it less than 5%.
3) Ideas include the small block size, hardware not using DMA, hardware
generating a lot of interrupts/only transferring a single sector at a time.
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