Messages in this thread | | | Date | Mon, 23 Apr 2018 09:47:42 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH tip/core/rcu 01/22] sched: Make non-production PREEMPT cond_resched() help Tasks RCU |
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On Mon, 23 Apr 2018 05:40:00 -0700 "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> 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/20180227153646.GD3777@linux.vnet.ibm.com
-- Steve
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