Re: top(1) behavior

[Martin Husemann <martin%duskware.de@localhost>]

On Fri, Aug 11, 2023 at 07:04:01PM -0700, Kevin Bowling wrote:
> A real example is doing a -j 8 kernel build.  Up in the top of top(1),
> I see global CPU usage in the high 90%.  Down in the process list, I
> see a few processes in the 1-10% range that do not add up to 800%.  I
> see some of the cc1 processes with 0% WCPU%/CPU%.

I am not sure I see what you mean, for me typically there are a few gcc
processes that take all the cpu, or later (close to the end) a few
xz or gzip processes. At a few spots ld wins and hogs at least one cpu
completely.

At least it looks not completely off, the top area displays statistics for
aggregated intervals, while many processes (besides the ones mentioned)
are very short lived - so the display is mostly what I'd expect it to be.

If you do "top -b" (so the list is not truncated) and save it to a file,
do you get a snapshot that is still unreasonable from your POV? Can you
share a concrete example?

For FreeBSD showing the values more like you expect I'd blame that on clang/
llvm being slow, but I'll be shot for this remark :-)

But still specualting without data: one thing that could make a serious
difference is the device you are running your build.sh on having a
suboptimal driver spending a lot of cpu in the kernel for the IO the
build produces.

Martin