On Fri, May 12, 2017 at 11:38 AM, Andi Kleen <a...@firstfloor.org> wrote:
> From: Andi Kleen <a...@linux.intel.com>
>
> 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?
Ok. Can you retain -o perf.data (even if that's the default)?
Thanks,
Richard.
> gcc/testsuite/:
>
> 2017-05-12 Andi Kleen <a...@linux.intel.com>
>
> PR testsuite/77684
> * lib/target-supports.exp (profopt-perf-wrapper): Remove
> -p perf.data option. Add -m8 option.
> ---
> gcc/testsuite/lib/target-supports.exp | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/gcc/testsuite/lib/target-supports.exp
> b/gcc/testsuite/lib/target-supports.exp
> index 83e7f2670e6..a22657767db 100644
> --- a/gcc/testsuite/lib/target-supports.exp
> +++ b/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/perfe_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 -m8 "
> }
>
> # Return true if profiling is supported on the target.
> --
> 2.12.2
>
