On 05/18/2017 02:39 AM, Richard Biener wrote: > On Thu, May 18, 2017 at 10:35 AM, Aldy Hernandez <al...@redhat.com> wrote: >> Andi Kleen <a...@firstfloor.org> writes: >> >>> 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 >> >> So for -jN > 16 it would silently fail again? >> >> I think we should warn when the -jN is sufficiently large such that >> tests will randomly fail, and perhaps suggest workarounds with >> ulimit/etc. > > given that make check parallelism is somewhat "explicit" can't we > simply arrange for the chunks to never get more than, say, 4 tree-prof.exp > testcases run at the same time? That would be significantly better than warning.
jeff
