selftests/bpf: Avoid spurious spmc parallel selftest errors in libarena

The libarena parallel spmc selftest is nondeterministic by design. As a result it depends up to a point on the relative timing between the producer and consumer threads. This introduces the possibility for two kinds of spurious failures that this patch addresses. 1) Spurious timeouts. The test proceeds in phases, and threads use a common counter as a barrier to avoid proceeding to the next phase until all threads are ready to do so. If a thread takes too long to reach the barrier, the already waiting threads may time out. Increase the current timeout. The timeout's value is a balance between the maximum amount of time spent on the test and the possibility of spurious failures. Right now the timeout is too short. Err on the side of caution and significantly increase it to avoid spurious failures. 2) Spurious resize failures. Some selftests require the spmc queue to resize itself. This in turn requires for the producer side to be materially faster than the consumer side so that the queue gets full enough for a resize. However, in the benchmark the spmc queue's producer is outnumbered 3:1. To offset it we add busy waits for consume queues. However, we still see occasional failures due to the queue never resizing. Minimize the possibility for this in two ways: First, remove one of the consumers. The 2 consumers still exercise the "race between consumers" scenario. Second, increase the busy wait duration to decrease the rate by which the consumers act on the queue. While at it, also replace a stray invalid error value "153" with EINVAL.

ETEmil Tsalapatis committed 5 months ago