perf tools: Make the mmap length autotuning more robust

Commit-ID:  1be300f4cc1ddf975f158b4ab2f880854b29306b
Gitweb:     http://git.kernel.org/tip/1be300f4cc1ddf975f158b4ab2f880854b29306b
Author:     Arnaldo Carvalho de Melo <[email protected]>
AuthorDate: Tue, 16 Dec 2014 12:19:00 -0300
Committer:  Arnaldo Carvalho de Melo <[email protected]>
CommitDate: Wed, 17 Dec 2014 11:58:14 -0300

perf tools: Make the mmap length autotuning more robust

If /proc/sys/kernel/perf_event_mlock_kb is not (power of 2 + PAGE_SIZE_in_kb) and we let the perf tools do mmap length autosizing based on that, then, for non-CAP_IPC_LOCK users when /proc/sys/kernel/perf_event_paranoid is > -1, then we get an -EINVAL that ends up in:

[acme@ssdandy linux]$ trace usleep 1
Invalid argument
[acme@ssdandy linux]$ perf record usleep 1
failed to mmap with 22 (Invalid argument)

After this fix:

[acme@ssdandy linux]$ trace usleep 1
<SNIP>
0.806 ( 0.006 ms): munmap(addr: 0x7f7e4740a000, len: 66467) = 0

   0.869 ( 0.002 ms): brk(                                   ) = 0x7bb000
   0.873 ( 0.003 ms): brk(brk: 0x7dc000                      ) = 0x7dc000
   0.877 ( 0.001 ms): brk(                                   ) = 0x7dc000
   0.953 ( 0.058 ms): nanosleep(rqtp: 0x7fff26ab9420         ) = 0

0.959 ( 0.000 ms): exit_group(
[acme@ssdandy linux]$ perf record usleep 1
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.017 MB perf.data (~759 samples) ] [acme@ssdandy linux]$

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

index 8eb92cf..7d88327 100644
@@ -909,6 +909,8 @@ static size_t perf_evlist__mmap_size(unsigned long pages)
 		}
 
 		pages = (max * 1024) / page_size;
+		if (!is_power_of_2(pages))
+			pages = rounddown_pow_of_two(pages);
 	} else if (!is_power_of_2(pages))
 		return 0;