debugtrace: add per-cpu buffer option

debugtrace: add per-cpu buffer option

debugtrace is normally writing trace entries into a single trace
buffer. There are cases where this is not optimal, e.g. when hunting
a bug which requires writing lots of trace entries and one cpu is
stuck. This will result in other cpus filling the trace buffer and
finally overwriting the interesting trace entries of the hanging cpu.

In order to be able to debug such situations add the capability to use
per-cpu trace buffers. This can be selected by specifying the
debugtrace boot parameter with the modifier "cpu:", like:

  debugtrace=cpu:16

At the same time switch the parsing function to accept size modifiers
(e.g. 4M or 1G).

Printing out the trace entries is done for each buffer in order to
minimize the effort needed during printing. As each entry is prefixed
with its sequence number sorting the entries can easily be done when
analyzing them.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>