On Mon, 21 Nov 2016 18:18:53 +0100 Peter Zijlstra <pet...@infradead.org> wrote:
> Its not ftrace as such though, its RCU, ftrace simply uses RCU to avoid > locking, as one does. Just to be clear, as ftrace in the kernel mostly represents function tracing, which doesn't use RCU. This is a tracepoint feature. > > Biggest objection would be that the rcu_irq_enter_irqson() thing does > POPF and rcu_irq_exit_irqson() does again. So wrapping every tracepoint > with that is quite a few cycles. Agree. Even though this ends up being a whack-a-mole(TM) fix, I'm not concerned enough to put a heavy weight rcu idle code in for all tracepoints. Although, what about a percpu flag that can be checked in the tracepoint code to see if it should enable RCU or not? Hmm, I wonder if "rcu_is_watching()" is light enough to have in all tracepoints? -- Steve
