On Mon, 23 Apr 2018 05:40:00 -0700 "Paul E. McKenney" <[email protected]> wrote:
> > I'm confused.. why is having this conditional on TRACEPOINT_BENCHMARK a > > sane idea? > > Because the TRACEPOINT_BENCHMARK tests are insane, so a similar > level of insanity is required to make things work. Plus having this > be unconditional would not be good for performance, as 0day has been > telling me frequently over the past couple of years. Just for some context. The tracepoint benchmark (which should never be enabled in any production machine), will start a thread when the benchmark trace event is enabled. This thread will never exit (until the trace event is disabled), and does a benchmark loop and constantly calls "cond_resched()" to allow other tasks to run. The point is, this thread will never have a quiescent state for task_rcu, unless we tell rcu that cond_resched() is a quiescent state. But this is only required because the tracepoint benchmark has this nasty thread, that is only used for debugging and benchmarking the tracepoint (during development). I also suggested having a direct call into RCU from the thread to tell RCU that it entered a quiescent state, but Paul didn't like that idea as it caused the tracepoint benchmark to call too deep into RCU internals. http://lkml.kernel.org/r/[email protected] -- Steve
