Limit perf data buffer during profiling

With high -j parallelism the autofdo tests can randomly fail.
autofdo uses Linux perf to record profiling data.
Linux perf uses a locked perf buffer. By default it has
around 516k buffer per uid (/proc/sys/kernel/perf_event_mlock_kb).

An individual perf record tries to grab the full 516k,
which makes parallel perf record fail.

This patch limits the perf buffer for individual perf record to 8k.
With the default settings this allows a parallelism of the test
cases of 16, which is hopefully good enough

(if not would need to add some kind of semaphore, or ask
the user to increase the limit as root)

I also removed an unneeded -o perf.data option

Thanks to Marcin to finally spotting the problem.

Passes bootstrap and test on x86_64-linux. Ok for trunk?

gcc/testsuite/:

2017-05-12  Andi Kleen  <ak@linux.intel.com>

	PR testsuite/77684
	* lib/target-supports.exp (profopt-perf-wrapper):
	Add -m8 option to increase parallelism.

From-SVN: r247962

gcc/testsuite/ChangeLog

+2017-05-12  Andi Kleen  <ak@linux.intel.com>
+
+	PR testsuite/77684
+	* lib/target-supports.exp (profopt-perf-wrapper):
+	Add -m8 option to increase parallelism.
+
 2017-05-12  Thomas Schwinge  <thomas@codesourcery.com>
 
 	* c-c++-common/goacc/parallel-dims-1.c: New file.

gcc/testsuite/lib/target-supports.exp

@@ -522,9 +522,16 @@ proc check_effective_target_keeps_null_pointer_checks { } {
 
 # Return the autofdo profile wrapper
 
+# Linux by default allows 516KB of perf event buffers
+# in /proc/sys/kernel/perf_event_mlock_kb
+# Each individual perf tries to grab it
+# This causes problems with parallel test suite runs. Instead
+# limit us to 8 pages (32K), which should be good enough
+# for the small test programs. With the default settings 
+# this allows parallelism of 16 and higher of parallel gcc-auto-profile
 proc profopt-perf-wrapper { } {
     global srcdir
-    return "$srcdir/../config/i386/gcc-auto-profile -o perf.data "
+    return "$srcdir/../config/i386/gcc-auto-profile -o perf.data -m8 "
 }
 
 # Return true if profiling is supported on the target.