stackcollapse-perf: fix flag in example

[wolfgang42]

Looks like the intent was to pass --fields, not --force.

I was already confused when I started reading the docs for this script, using the wrong option didn't help matters any ;-)

[brendangregg]

No, please see lines 115 to 118 -- the docs should match the usage message.

[wolfgang42]

Well, that's confusing, it depends on the kernel version?:

FlameGraph/stackcollapse-perf.pl

Lines 115 to 118 in 15c0c57

	[1] perf script must emit both PID and TIDs for these to work; eg, Linux < 4.1:
	perf script -f comm,pid,tid,cpu,time,event,ip,sym,dso,trace
	for Linux >= 4.1:
	perf script -F comm,pid,tid,cpu,time,event,ip,sym,dso,trace

Ah, I see, the meaning of -f was changed in 4.1:

And -f is already taken up by --fields, which makes --force confused, so change the short option name of --fields to -F like what other perf commands do (e.g. perf report -F) and use -f as the short option name of --force.

In that case, would you instead accept a patch to just change the docs in this file to use the long option --fields and skip the short option confusion altogether? It looks to me like that should work back to 2.6.39 when custom field selection was introduced.