[Crash-utility] [PATCH] Display online cpus value in preference to kt->cpus

[Dave Anderson]

----- "Luciano Chavez" <lnx1138 at linux.vnet.ibm.com> wrote:

> Hi Dave,
> 
> Thinking about backward compatibility, would displaying "ONLINE CPUS"
> still seem OK for the case where kernel_init() finds the smp_num_cpus
> symbol (as for a 2.4 kernel)? Before there were the various cpu maps, I
> think smp_num_cpus was analogous to the possible cpus as opposed to
> online. I can see this requiring some thought as to what CPUS in the
> output means when you have various different maps now (online, possible,
> and present). That being said, it would be good to leave no doubt and
> explicitly state the count is for the present or online CPUS with the
> latter being my suggestion.
> 
> I forgot to mention that I suspect the problem I mentioned before would
> get stranger for POWER7 which offers 4 threads per core. I didn't have
> access to a POWER7 machine to see just what it would do if we tried
> disabling SMT as before but it follows the same pattern the count
> displayed would be way off from the online count.

I just ran through a bunch of stashed dumpfiles I have on hand, and
it gets even murkier when dealing with Xen or KVM kernels, because
as part of the post-crash shutdown (or forced dump), all but one of
the cpus may be taken "offline".  So even though there may be 4 vcpus,
and crash correctly shows 4 "CPUS", the cpu_online_map shows only one
cpu bit.  So if we went ahead and displayed a number based upon the
cpu_online_map, it would completely misleading.  Incorrect actually...

Dave