Re: [PATCH v15 04/13] task_isolation: add initial support
From: Paul E. McKenney <hidden>
Date: 2016-09-27 14:48:18
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On Tue, Sep 27, 2016 at 04:22:20PM +0200, Frederic Weisbecker wrote:
On Fri, Sep 02, 2016 at 10:28:00AM -0700, Andy Lutomirski wrote:quoted
Unless I'm missing something (which is reasonably likely), couldn't the isolation code just force or require rcu_nocbs on the isolated CPUs to avoid this problem entirely.rcu_nocb is already implied by nohz_full. Which means that RCU callbacks are offlined outside the nohz_full set of CPUs.
Indeed, at boot time, RCU makes any nohz_full CPU also be a rcu_nocb CPU.
quoted
I admit I still don't understand why the RCU context tracking code can't just run the callback right away instead of waiting however many microseconds in general. I feel like paulmck has explained it to me at least once, but that doesn't mean I remember the answer.The RCU context tracking doesn't take care of callbacks. It's only there to tell the RCU core whether the CPU runs code that may or may not run RCU read side critical sections. This is assumed by "kernel may use RCU, userspace can't".
And RCU has to wait for read-side critical sections to complete before invoking callbacks. Thanx, Paul -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>