perf evlist: Fixup brown paper bag on "hint" for --mmap-pages cmdline arg

Commit-ID:  0a2138b28fd56eeb3852133691c881409885ee3f
Gitweb:     http://git.kernel.org/tip/0a2138b28fd56eeb3852133691c881409885ee3f
Author:     Arnaldo Carvalho de Melo <[email protected]>
AuthorDate: Fri, 12 Dec 2014 16:07:47 -0300
Committer:  Arnaldo Carvalho de Melo <[email protected]>
CommitDate: Tue, 16 Dec 2014 13:38:26 -0300

perf evlist: Fixup brown paper bag on "hint" for --mmap-pages cmdline arg

When failing due to asking for a number of mmap pages that is more than the max, it was suggesting that an even bigger number of mmap pages should be specified, doh, au contraire!

Before:

[acme@ssdandy linux]$ trace -m 128 usleep 1
Error: Operation not permitted.
Hint: Check /proc/sys/kernel/perf_event_mlock_kb (516 kB) setting.
Hint: Tried using 516 kB.
Hint: Try using a bigger -m/--mmap-pages value.
[acme@ssdandy linux]$

After:

[acme@ssdandy linux]$ trace -m 128 usleep 1
Error: Operation not permitted.
Hint: Check /proc/sys/kernel/perf_event_mlock_kb (516 kB) setting.
Hint: Tried using 516 kB.
Hint: Try using a smaller -m/--mmap-pages value.
[acme@ssdandy linux]$

And to (really) clarify what happens above, when what the user requests is <= max and even then it fails, a changeset is being made to tell that this is a per user limit, not per process (in the above example there was another 'perf trace' running for this user, which was using all the pages it could use).

---
 tools/perf/util/evlist.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index bb5dfc5..de7515d 100644
@@ -1495,7 +1495,7 @@ int perf_evlist__strerror_mmap(struct perf_evlist *evlist, int err, char *buf, s
 		scnprintf(buf, size, "Error:\t%s.\n"
 				     "Hint:\tCheck /proc/sys/kernel/perf_event_mlock_kb (%d kB) setting.\n"
 				     "Hint:\tTried using %zd kB.\n"
-				     "Hint:\tTry using a bigger -m/--mmap-pages value.",
+				     "Hint:\tTry using a smaller -m/--mmap-pages value.",
 				     emsg, value, evlist->mmap_len / 1024);
 		break;
 	default: