[Crash-utility] Question on online/present/possible CPUs

[Petr Tesarik]

Hi all,

before making a larger cleanup, I want to ask here for your opinion. It
seems that there is quite a bit of confusion about the meaning of CPU
count printed out by the crash utility.

1. Number of CPUs

Some people think that crash should always output the number of CPUs in
the system (ie. a quad-core server should always output 'CPUS: 4'),
while other people think that only online CPUs should be counted.

2. CPU numbering

For example, if there are 4 CPUs in the system, but some of them are
taken offline (e.g. CPU 1 and CPU 3), _and_ crash output the number of
online CPUs, it would print out 'CPUS: 2'. It's not easy to find out
that valid CPU numbers are 0 and 2 in this case.

3. Examining offline CPU

Sometimes, it may be useful to examine the state of an offline CPU. Now,
I know that the saved state is most likely stale, but it can be useful
in some cases (e.g. a crash after dropping to kdb). The crash utility
currently refuses to select an offline CPU with 'set -c #'. Are there
any concerns about allowing it?

Regards,
Petr Tesarik