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Date: Thu, 2 Apr 2015 20:08:03 +0200 From: Oleg Nesterov <oleg@...hat.com> To: Frederic Weisbecker <fweisbec@...il.com> Cc: LKML <linux-kernel@...r.kernel.org>, Peter Zijlstra <peterz@...radead.org>, Dave Jones <davej@...hat.com>, Thomas Gleixner <tglx@...utronix.de>, "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>, Ingo Molnar <mingo@...nel.org>, Rik van Riel <riel@...hat.com> Subject: Re: [PATCH 2/3] context_tracking: Inherit TIF_NOHZ through forks instead of context switches On 04/02, Frederic Weisbecker wrote: > > +void context_tracking_cpu_set(int cpu) > { > - clear_tsk_thread_flag(prev, TIF_NOHZ); > - set_tsk_thread_flag(next, TIF_NOHZ); > + static bool initialized = false; > + struct task_struct *p, *t; > + unsigned long flags; > + > + if (!per_cpu(context_tracking.active, cpu)) { > + per_cpu(context_tracking.active, cpu) = true; > + static_key_slow_inc(&context_tracking_enabled); > + } > + > + if (initialized) > + return; > + > + set_tsk_thread_flag(&init_task, TIF_NOHZ); > + > + /* > + * There shouldn't be any thread at this early boot stage > + * but the scheduler is ready to host any. So lets walk > + * the tasklist just in case. tasklist_lock isn't necessary > + * either that early but take it for correctness checkers. > + */ > + read_lock_irqsave(&tasklist_lock, flags); > + for_each_process_thread(p, t) > + set_tsk_thread_flag(t, TIF_NOHZ); > + read_unlock_irqrestore(&tasklist_lock, flags); > + > + initialized = true; > } Agreed, but _irqsave is not needed. read_lock(tasklist) should work just fine. Any reason 3/3 comes as a separate change? I won't argue, just curious. Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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